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VOL.   I 

New  Tork 

The  Macmillan  Co. 



Cambridge  University  Press 

Bombay,  Calcutta  and 


Macmillan  and  Co.,  Ltd. 


The  Macmillan  Co.  of 

Canada,  Ltd. 

All  rights  reserved 


f)      ^ 


Vir  PraecLarissinius 


Mysterii  Generationis  Indaqator  Diliqens. 

Q)  r^^Lji(iJ<^i~^4^(tJ^^^i~^^L3(*J<^^>^L3(*^^  0 




M. A.,  Ph.D. 

Fellow  ofGonville  &  Cains  College,  Cambridge,  and 

University  Demonstrator  in 





3  'j>^t>r^<?>^t>r^)(r>^t>f7)(j>^t>r^cp^<jt>^  ^ 



in  Univ.  Aberdon.  Anat.  olim  Professori 


Schol.  Undel.  olim  Praeposito 


Coll.  Gonv.  et  Caii  olim  Custodi 


Artis  chemicae  ad  animantia  spectantis  in 
Univ.  Cantabrig.  Professori 


hanc  suam  disquisitionem 


sacram  voluit 

For  more,  and  abler  operations  are  required  to  the  Fabrick 
and  erection  of  Living  creatures,  than  to  their  dissolution, 
and  plucking  of  them  down :  For  those  things  that  easily 
and  nimbly  perish,  are  slow  and  difficult  in  their  rise  and 

William  Harvey,  Anatomical  Exercitations  concerning 
the  generation  of  living  creatures,  London,  1653, 
Ex.  XLi,  p.  206. 

That  discouraging  Maxime,  Nil  dictum  quod  non 
dictum  prius,  hath  little  room  in  my  estimation,  nor  can 
I  tye  up  my  belief  to  the  Letter  of  Solomon  ;  I  do  not  think, 
that  all  Science  is  Tautology;  these  last  Ages  have  shown 
us,  what  Antiquity  never  saw;  no,  riot  in  a  dream. 

Joseph  Glanville,  Scepsis  Scientifica,  an  essay  of  the 
vanity  of  dogmatizing,  and  confident  opinion,  London, 
1 66 1,  Chap.  XXII. 



Prolegomena  page  2 

PART    I 

The  Theory  of  Chemical  Embryology 

Philosophy,  Embryology,  and  Chemistry  7 

The  Historical  Perspective  10 

Obstacles  to  Chemical  Embryology  1 3 

The  Stumbling-block  of  Hormism  1 4 

Finalism  as  a  Rock  of  Offence  1 6 

Organicism  as  an  Occasion  of  Falling  25 

Organicism  and  Emergence  3^ 

Neo-Mechanism  as  a  Theory  for  Chemical  Embryology  32 


The  Origins  of  Chemical  Embryology 

Preliminary  Note  41 

Section  i .  Embryology  in  Antiquity  44 

I  •  I .  Non-Hellenic  Antiquity  44 

1-2.  Hellenic  Antiquity;  the  Pre-Socratics  50 

1-3.  Hippocrates;  the  Beginning  of  Observation  53 

1-4.  Aristotle  ^g 

1-5.  The  Hellenistic  Age  77 

1-6.  Galen  85 

Section  2.  Embryology  from  Galen  to  the  Renaissance  gi 

2-1.  Patristic,  Talmudic,  and  Arabian  Writers  gi 

2-2.  St  Hildegard;  the  Lowest  Depth  g^ 

23.  Albertus  Magnus  gy 

2-4.  The  Scholastic  Period  103 

2-5.  Leonardo  da  Vinci  1 07 

2-6.  The  Sixteenth  Century;  the  Macro-iconographers  I  lO 

NE  h 

'>  i 

/  i\  '\  ^     , 



Section  3.  Embryology  in  the  Seventeenth  and  Eighteenth  Centuries  page  125 

3-1.     The  Opening  Years  of  the  Seventeenth  Century  1 25 

32.     Kenelm  Digby  and  Nathaniel  Highmore  1 29 

3-3.     Thomas  Browne  and  the  Beginning  of  Chemical  Embryology  135 

3-4.     William  Harvey  138 

35,  Gassendi  and  Descartes;  Atomistic  Embryology  1 56 

36.  Walter  Needham  and  Robert  Boyle  1 60 
3-7.  Marcello  Malpighi;  Micro-iconography  and  Preformationism  166 
3-8.  Robert  Boyle  and  John  Mayow  169 
3-9.  The  Theories  of  Foetal  Nutrition  176 
3-10.  Boerhaave,  Hamberger,  Mazin  1 82 
3-11.  Albrecht  v.  Haller  and  his  Contemporaries  1 88 
3-12.  Ovism  and  Animalculism  1 99 
3- 1 3.  Preformation  and  Epigenesis  205 
3-14.  The  Close  of  the  Eighteenth  Century  215 
3-15.  The  Beginning  of  the  Nineteenth  Century  220 


General  Chemical  Embryology 

Preliminary  Note 

Section  i.  The  UnfertiUsed  Egg  as  a  Physico-chemical  System 

1 .  Introduction 

2.  General  Characteristics  of  the  Avian  Egg 

3.  The  Proportion  of  Parts  in  the  Avian  Egg 

4.  Chemical  Constitution  of  the  Avian  Egg  as  a  Whole 

5.  The  Shell  of  the  Avian  Egg 

6.  The  Avian  Egg-white 

7.  The  Avian  Yolk 

8.  The  Avian  Yolk-proteins 

9.  The  Fat  and  Carbohydrate  of  the  Avian  Yolk 

10.  The  Ash  of  the  Avian  Egg 

1 1 .  General  Characteristics  of  non-Avian  Eggs 

12.  Egg-shells  and  Egg-membranes 

13.  Proteins  and  other  Nitrogenous  Compounds 

14.  Fats,  Lipoids,  and  Sterols 

15.  Carbohydrates 

16.  Ash 







Section  2.  On  Increase  in  Size  and  Weight 

page  368 

2-1.  Introduction 

2-2.  The  Existing  Data  369 

2-3.  The  General  Nature  of  Embryonic  Growth  383 

2-4.  The  Empirical  Formulae  389 

2-5.  Percentage  Growth-rate  and  the  Mitotic  Index  399 

2-6.  Yolk-absorption  Rate  405 

2 '7.  The  Autocatakinetic  Formulae  408 

2-8.  Instantaneous  Percentage  Growth-rate  420 

2-9.  Growth  Constants  434 

2-10.  The  Growth  of  Parts  440 

2-1 1.  Variability  and  Correlation  455 

2-12.  Explantation  and  the  Growth-promoting  Factor  460 

2-13.  Incubation  Time  and  Gestation  Time  470 

2-14.  The  Effect  of  Heat  on  Embryonic  Growth  498 

2-15.  Temperature  Coefficients  503 

2  •  1 6.  Temperature  Characteristics  515 

2-17.  The  Effect  of  Light  on  Embryonic  Growth  533 

2-i8.  The  Effect  of  X-rays  and  Electricity  on  Embryonic  Growth      536 

2-19.  The  Effect  of  Hormones  on  Embryonic  Growth  538 

Section  3. 





On  Increase  in  Complexity  and  Organisation 
The  Independence  of  Growth  and  Differentiation 

Chemical  Processes  and  Organic  Form 
The  Types  of  Morphogenetic  Action 
Pluripotence  and  Totipotence 
Self-differentiation  and  Organiser  Phenomena 
Functional  Differentiation 
Axial  Gradients 
Organised  and  Unorganised  Growth 

3-10.  Chemical  Embryology  and  Genetics 



Section  4.   The  Respiration  and  Heat-production  of  the  Embryo  615 

4- 1 .     Early  Work  on  Embryonic  Respiration  6 1 5 

4-2.     Respiration  of  Echinoderm  Embryos  in  General  623 

4-3.     Rhythms  in  Respiratory  Exchange  64 1 



Section  4-4.    Heat  Production  and  Calorific  Quotients  of  Echinoderm    page  649 

4-5.     Respiration   of  Annelid,   Nematode,   Rotifer,   and   Mollusc      659 

46.  Respiration  of  Fish  Embryos  665 

47.  ,  Respiration  of  Amphibian  Embryos  67 1 
4-8.  Heat-production  of  Amphibian  Embryos  682 
49.  Respiration  of  Insect  Embryos  687 
4- 1  o.  Respiration  of  Reptile  Embryos  692 
4-11.  Respiration  of  Avian  Embryos  in  General  693 
4-12.  Heat-production  of  Avian  Embryos  7^4 
4-13.  Later  Work  on  the  Chick's  Respiratory  Exchange  7^8 
4- 1 4.  The  Air-space  and  the  Shell  7 1 9 
4-15.  Respiration  of  Mammalian  Embryos  726 
4"  1 6.  Heat-production  of  Mammalian  Embryos  732 
4-17.  Anaerobiosis  in  Embryonic  Life  742 

^,     4"  1 8.  Metabolic  Rate  in  Embryonic  Life  746 

4-19.  Respiratory  Intensity  of  Embryonic  Cells  fn  wVro  755 

4-20.  Embryonic  Tissue-respiration  and  Glycolysis  758 

4-21.  The  Genesis  of  Heat  Regulation  772 

4-22.  Light-production  in  Embryonic  Life  776 

Section  5.   Biophysical  Phenomena  in  Ontogenesis  777 

5-1.     The  Osmotic  Pressure  of  Amphibian  Eggs  777 

5-2.     The  Genesis  of  Volume  Regulation    ,  786 

53.  The  Osmotic  Pressure  of  Aquatic  Arthropod  Eggs  790 

54.  The  Osmotic  Pressure  of  Fish  Eggs  793 

5-5.     Osmotic  Pressure  and  Electrical  Conductivity  in  Worm  and      799 
Echinoderm  Eggs 

5-6.     The  Osmotic  Pressure  of  Terrestrial  Eggs  8l2 

5-7.     Specific  Gravity  820 

5-8.     Potential  Differences,  Electrical  Resistance,  Blaze  Currents      825 
and  Cataphoresis 

5-9.     Refractive  Index,  Surface  Tension  and  Viscosity  833 

Section  6.   General  Metabolism  of  the  Embryo  839 

6-1.     The  j&H  of  Aquatic  Eggs  839 

6-2.     The  j&H  of  Terrestrial  Eggs  855 

63.     rH  in  Embryonic  Life  865 

6-4.     Water-metabolism  of  the  Avian  Egg  870 


Section  6-5.     Water-content  and  Growth-rate  page  883 

6-6.     Water-absorption  and  the  Evolution  of  the  Terrestrial  Egg  889 

6-7.     Water-metabolism  in  Aquatic  Eggs  906 

6-8.     The  Chemical  Constitution  of  the  Embryonic  Body  in  Birds      911 
and  Mammals 

69.     Absorption-mechanisms  and  Absorption-intensity  917 

6- 10.  Storage  and  Combustion;  the  Plastic  Efficiency  Coefficient  934 

6-1 1.  Metabolism  of  the  Avian  Spare  Yolk  939 

6-12.  Maternal  Diet  and  Embryonic  Constitution  943 

Section  7.  The  Energetics  and  Energy-sources  of  Embryonic  Development  946 

7-1.     The  Energy  Lost  from  the  Egg  during  Development  946 

7-2.     Energy  of  Growth  and  Energy  of  Differentiation  956 

7-3.     The  Relation  between  Energy  Lost  and  Energy  Stored  962 

7-4.     Real  Energetic  Efficiency                                     •  969 

7-5.     Apparent  Energetic  Efficiency  972 

7*6.     Synthetic  Energetic  Efficiency  98 1 

7-7.     The  Sources  of  the  Energy  Lost  from  the  Egg  986 

Sections.  Carbohydrate  Metabolism  1000 

8-1.     General  Observations  on  the  Avian  Egg  lOOO 

8-2.     Total  Carbohydrate,  Free  Glucose,  and  Glycogen  lOOl 

8-3.     Ovomucoid  and  Combined  Glucose  1 007 

8-4.     Carbohydrate  and  Fat  1014 

8-5.  The  Metabolism  of  Glycogen  and  the  Transitory  Liver  1018 
8-6.  Free  Glucose,  Glycogen,  and  Insulin  in  the  Embryonic  Body  IO29 
8-7.     General  Scheme  of  Carbohydrate  Metabolism  in  the  Avian  Egg    1035 

8-8.     Embryonic  Tissue  Glycogen  1 036 

8'9.     Embryonic  Blood  Sugar  1039 

8- 10.  Carbohydrate  Metabolism  in  Amphibian  Development  1043 

8*i  I.  Carbohydrate  Metabolism  of  Invertebrate  Eggs  I047 

8-12.  Pentoses  1 05 1 

8-13.  Lactic  Acid  1 051 

8-14.  Fructose  1054 

Section  9.  Protein  Metabolism  1055 

9* I.     The  Structure  of  the  Avian  Egg-proteins  before  and  after  1055 


9*2.     Metabolism  of  the  Individual  Amino-Acids  I059 

9-3.     The  Relations  between  Protein  and  non-Protein  Nitrogen  1065 

9-4.     The  Accumulation  of  Nitrogenous  Waste  Products  10 76 


Section  9-5.  Protein  Catabolism  page 

9-6.  Nitrogen-excretion;  Mesonephros,  Allantois,  and  Amnios 

9-7.  The  Origin  of  Protective  Syntheses 

9*8.  Protein  Metabolism  of  Reptilian  Eggs 

9-9.  Protein  Metabolism  of  Amphibian  Eggs 

9' 10.  Protein  Metabolism  in  Teleostean  Ontogeny 

9-11.  Protein  Metabolism  in  Selachian  Ontogeny 

9*  1 2.  Protein  Metabolism  of  Insect,  Worm,  and  Echinoderm  Eggs 

9-13.  Protein  Utilisation  in  Mammalian  Embryonic  Life 

9-14.  Protein  Utilisation  of  Explanted  Embryonic  Cells 

9-15.  Uricotelic  Metabolism  and  the  Evolution  of  the  Terrestrial  Egg 

Section  10.  The  Metabolism  of  Nucleins  and  Nitrogenous  Extractives 

[O-i.  Nuclein  Metabolism  of  the  Chick  Embryo 

IO-2.  The  Nucleoplasmatic  Ratio 

[0-3.  Nuclein  Synthesis  in  Developing  Eggs 

[0-4.  Creatinine,  Creatine,  and  Guanidine 

Section  11.  Fat  Metabolism 

I  •  I .  Fat  Metabolism  of  Avian  Eggs 

1-2.  Fat  Metabolism  of  Reptilian  Eggs 

I  •2-  Fat  Metabolism  of  Amphibian  Eggs 

I  -4.  Fat  Metabolism  of  Selachian  Eggs 

1-5.  Fat  Metabolism  of  Teleostean  Eggs 

1-6.  Fat  Metabolism  of  Mollusc,  Worm,  and  Echinoderm  Eggs 

1-7.  Fat  Metabolism  of  Insect  Eggs 

1-8.     Combustion  and   Synthesis  of  Fatty  Acids  in  Relation   to 
Metabolic  Water 

1 1  -9.     Fat  Metabolism  of  Mammalian  Embryos 

Section  12.  The  Metabolism  ofLipoids,  Sterols,  Cycloses,  Phosphorus 
and  Sulphur 

1 2- 1.  Phosphorus  Metabolism  of  the  Avian  Egg 

12-2.  Tissue  Phosphorus  Coefficients 

I2'3.  Choline  in  Avian  Development 

12-4,  The  Metabolism  of  Sterols  during  Avian  Development 

1 2*5.     The  Relation  between  Lipoids  and  Sterols;  the  Lipocytic 

12-6.     Cycloses  and  Alcohols  in  Avian  Development 

12-7.     Sulphur  Metabolism  of  the  Avian  Egg 

12-8.     Phosphorus,  Sulphur,  Choline,  and  Cholesterol  in  Reptile  Eggs 


Section  12-9.  Lipoids  and  Sterols  in  Amphibian  Eggs  page  1237 

12-10.  Lipoids,  Sterols,  and  Cycloses  in  Fish  Eggs  1239 

i2'ii.  Phosphorus,  Lipoids  and  Sterols  in  Arthropod  Eggs  1241 

12-12.  Phosphorus,  Lipoids,  and  Sterols  in  Worm  and  Echinoderm    1243 


12-13.  Lipoids  and  Sterols  in  Mammalian  Development  1252 

Section  13.  Inorganic  Metabolism  1255 

[  3- 1 .  Changes  in  the  Distribution  of  Ash  during  Avian  Development   1 255 

32.  Calcium  Metabolism  of  the  Avian  Egg  1260 

33.  Inorganic  Metabolism  of  other  Eggs  1 268 
3-4.  The  Absorption  of  Ash  from  Sea-water  by  Marine  Eggs  1 27 1 
3-5.  The  Ani on/Cation  Ratio  1 2  74 
3-6.  Inorganic  Metabolism  of  Mammalian  Embryos  1277 
3-7.  Calcium  Metabolism  of  Mammalian  Embryos  1285 

Section  14.   Enzymes  in  Ontogenesis  1289 

4-1.  Introduction  1 289 

4-2.  Enzymes  in  Arthropod  Eggs  1290 

4-3.  Enzymes  in  Mollusc,  Worm,  and  Echinoderm  Eggs  1293 

4-4.  Enzymes  in  Fish  Eggs  1 295 

4-5.  Enzymes  in  Amphibian  Eggs  1300 

4-6.  Enzymes  in  Sauropsid  Eggs  1303 

4-7.  Changes  in  Enzymic  Activity  during  Development  1307 

4-8.  Enzymes  of  the  Embryonic  Body  1 3^0 

4-9.  Enzymes  in  Mammalian  Embryos  13 12 

4-10.  The  Genesis  of  Nucleases  1326 

4-11.  Foetal  Autolysis  1 329 

Section  15.   Hormones  in  Ontogenesis  1335 

5-1.  Introduction  1335 

5-2.  Adrenalin  ^337 

53.  Insulin  1342 

5-4.  The  Parathyroid  Hormone  134^ 

5-5.  The  Hormones  of  the  Pituitary  134^ 

5-6.  Secretin  134^ 

5-7.  Thyroxin  134^ 

5-8.  Oestrin  and  other  Sex  Hormones                        •  1353 



Section  i6.  Vitamins  in  Ontogenesis  page  1359 

[6-1.  Vitamin  A  1359 

[6-2.  Vitamin  B  1360 

[6-3.  Vitamin  C  1 360 

[6-4.  Vitamin  D  1 360 

[6-5.  Vitamins  in  Mammalian  Development  1 363 

[6-6.  Vitamin  E  1 365 

Section  17.  Pigments  in  Ontogenesis  1368 

[7-1.  The  Formation  of  Blood  Pigments  1 368 

[7-2.  The  Formation  of  Bile  Pigments  137^ 

[7-3.  The  Formation  of  Tissue  Pigments  1 375 

[7-4.  The  Pigments  of  the  Avian  Egg-shell  137^ 

[7-5.  The  Pigments  of  the  Avian  Yolk  1378 

[7-6.  Egg-pigments  of  Aquatic  Animals  1380/ 

[7-7.  Melanins  in  Ontogenesis  13^^ 

Section  18.  Resistance  and  Susceptibility  in  Embryonic  Life  1383 

•I.  Introduction  1 3^3 

•2.  Standard  Mortality  Curves  1 3^3 

[8-3.  Resistance  to  Mechanical  Injury  ^3^5 

$-4.  Resistance  to  Thermal  Injury  1 388 

5-5.  Resistance  to  Electrical  Injury  ^392 

[8-6.  Resistance  to  Injury  caused  by  Abnormal  j&H  1 397 

5-7.  Resistance  to  Injury  caused  by  Abnormal  Gas  Concentrations     1 399 

(non-Avian  Embryos) 

!-8.  Critical  Points  in  Development  1 409 

!-g.  Resistance  to  Injury  caused  by  Abnormal  Gas  Concentrations     1 4 1 4 
(Avian  Embryos) 

>-io.  Resistance  to  Injury  caused  by  Toxic  Substances  1420 

••I  I.  Resistance  to  Injury  caused  by  X-rays,  Radium  Emanation,     1 43 1 
and  Ultra-violet  Light 

Section  19.  Serology  and  Immunology  in  Embryonic  Life  1444 

ig-i.  Antigenic  Properties  of  Eggs  and  Embryos  ^444 

19-2.  The  Formation  of  Natural  Antibodies  1446 

19-3.  The  Natural  Immunity  of  Egg-white  ^447 

19-4.  Inheritance  of  Immunity  in  Oviparous  Animals  HS^ 

19-5.  Serology  and  Pregnancy  1452 

19-6.  Resistance  of  the  Avian  Embryo  to  Foreign  Neoplasms  1 454 



Section  20.   Biochemistry  of  the  Placenta  page  14.^6 

20-1.     Introduction  1 45" 

20-2.     General  Metabolism  of  the  Placenta  145^ 

20-3.     Placental  Respiration  1 46 1 

20-4.     Nitrogen  Metabolism  of  the  Placenta  1 462 

20-5.     Carbohydrate  Metabolism  of  the  Placenta  14^9 

20-6.     Fat  and  Lipoid  Metabolism  of  the  Placenta  1472 

20-7.     Placental  Enzymes  1481 

Section  21.   Biochemistry  of  the  Placental  Barrier  1485 

2 1  •  I .     The  Autonomy  of  the  Foetal  Blood  1 4^5 

21-2.     Evolution  of  the  Placenta  -4^7 

21-3.     Histotrophe  and  Haemotrophe  149^ 

21-4.     Mesonephros  and  Placenta  1 493 

21-5.     Colostrum  and  Placenta  ^497 

21-6.     Placental  Transmission  and  Molecular  Size  1497 

21-7.     QuaHtative  Experiments  on  Placental  Permeability  1 505 

21-8.     The  Passage  of  Hormones  15^^ 

2 1  -9.     Factors  Governing  Placental  Transmission  15^2 

2I-IO.  Quantitative   Experiments   on   the  Passage  of  Nitrogenous     15 14 

2 1 -I  I.  Quantitative  Experiments  on  the  Passage  of  Phosphorus,  Fats,     1520 

and  Sterols 
2i'i2.  Quantitative  Experiments  on  the  Passage  of  Carbohydrates     1525 

2i*i3.  Quantitative  Experiments  on  the  Passage  of  Ash  1 52  7 

21-14.  The  Passage  of  Enzymes  15^9 

2i*i5.  The  Unequal  Balance  of  Blood  Constituents  1530 

Section  22.   Biochemistry  of  the  Amniotic  and  Allantoic  Liquids  1534 

22-1.     Introduction  1 534 

22-2.     Evolution  of  the  Liquids  ^535 

22-3.     Avian  Amniotic  and  Allantoic  Liquids  1 537 
22-4.     Amount  and  Composition  of  Mammalian  Amniotic  and  Allan-     1539 

toic  Liquids 

22-5.     Maternal  Transudation  and  Foetal  Secretion  154^ 

22-6.     Interchange  between  Amniotic  and  Allantoic  Liquids  15^2 

22-7.     Vernix  Caseosa  1 5^4 

Section  23.  Blood  and  Tissue  Chemistry  of  the  Embryo  1565 

23-1.    Blood  1565 

23-2.    Lung  1 57 1 

23-3.     Muscle  1574 



Section  23-4. 



Nervous  Tissue 


Connective  Tissue 




Sense  Organs 


Intestinal  Tract 

Section  24. 

Hatching  and  Birth 




Hatching  Enzymes 


Osmotic  Hatching 




Hatching  of  the  Avian  Egg 


MammaUan  Birth 

page  1577 





The  Two  Problems  of  Embryology  1 6 1 3 

The  Cleidoic  Egg  and  its  Evolution  16 1 3 

Chemical  Synthesis  as  an  Aspect  of  Ontogeny  1 623 

Biochemistry  and  Morphogenesis  1 624 

Transitory  Functions  in  Embryonic  Life  1627 

The  Theory  of  Recapitulation  1629 

Recapitulation  and  Substitution  '  1632 

Chemical  Recapitulation  1638 

Provisional  Generalisations  for  Chemical  Embryology  1 647 
The  Organisation  of  Development  and  the  Development  of  Organisation       1659 

The  Future  of  Embryology  1 664 



i.    Normal  Tables  of  Magnitudes  in  Embryonic  Growth  1669 

ii.    A  Chemical  Account  of  the  Maturation  of  the  Egg-cell  1679 

iii.  The   Chemical   Changes   during   the   Metamorphosis  of  Insects  (by  1685 

Dorothy  Needham) 

iv.  The  Development  of  the  Plant  Embryo  from  a  Physico-chemical  View-  1 7 1 1 

point  (by  Muriel  Robinson) 

PART    V 

Bibliography  and  Author-Index 


Index  Animalium 




William  Harvey frontispiece 

I.   Primitive  methods  of  incubation :  (A)  Egyptian,  (B)  Chinese  facing  page      46 
II.   The  oldest  known  drawing  of  the  Uterus  (gth  century)    .       „        „        82 

III.  Illustration  from  the  Liber  Scivias  of  St  Hildegard  (ca. 

1150A.D.) jj        J3        96 

IV.  A  page  from  Leonardo  da  Vinci's  Anatomical  Notebooks 

(ca.  1490  A.D.)      ........„„       108 

V.   Illustration  from  the  De  Formatione  Ovi  et  Pulli  of  Fabricius 

(1604) „        „       116 

VI.    Illustration  {rom  Highmore's  History  of  Generation  {16^1)  .       „        „       134 

VII.   Illustrations  from  Malpighi:  i)e  Or;o  in^M^a/o  (1672)  .       ,,        „       168 

VIII.   Reaumur's  Illustration  of  his  Incubators  (1749)       .         .       „        „       198 

IX.   Microphotograph  of  the  yolk  of  the  hen's  egg  at  the  time 

of  laying,  to  show  the  vitelline  globules  .         .  .         .       ,,         ,,       236 

X.    Microphotograph  of  the  yolk  of  the  hen's  egg,  not  yet 

liberated  from  the  ovary,  to  show  the  stratification .         .       „        ,,       288 


The  frontispiece  of  William  Harvey's  Generation  of  Ani- 
mals ( 1 65 1 ) ;  Zeus  liberating  living  beings  from  an  egg     .  frontispiece 

XI.  Microphotograph  of  the  yolk  of  the  hen's  egg  at  the 
eleventh  day  of  incubation,  showing  its  heterogeneous 
state    ..........  facing  page    836 

XII.   Microphotograph  of  the  yolk  of  the  hen's  egg  at  the  second 

day  of  incubation,  showing  the  cholesterol  esters     .         .       „        ,,1218 


An  embryological  investigation  in  the  eighteenth  century  frontispiece 


27.  Ash  of  the  avian  egg  .... 

34.  Distribution  of  amino-acids  in  egg-proteins 

47.  Ash  content  of  egg  . 

195.  Enzymes  in  the  hen's  egg 

199.  Enzymes  in  the  human  embryo 

201.  Enzymes  in  the  pig  embryo 

220.  Placental  enzymes    . 

227,  Passage  of  substances  through  the  placenta 
Appendix  1,  Table  3.    Embryonic  growth  of  the  hen 

facing  page 


»5                 55 


.J                 55 


55                 55 


55                 55 


55                 55 


55                 55 


55                 5' 


55                 5? 





THOSE  who  have  assisted  me  in  the  preparation  of  this  work  are  so 
numerous  that  it  is  impossible  to  mention  them  all  by  name.  Its 
original  impetus  was  derived  from  a  discussion  with  Professor  Sir 
F.  G.  Hopkins  in  1923  on  the  observation  of  Klein  that  inositol,  though 
absent  from  the  undeveloped  hen's  egg,  was  present  in  considerable 
quantity  at  hatching;  and  throughout  the  period  of  preparation  his 
encouragement,  help,  and  advice  were  never-failing.  I  have  derived  great 
benefit  from  the  discussion  of  various  points  with  Miss  Marjory  Stephenson, 
M.  Louis  Rapkine,  Dr  R.  A.  Fisher,  and  my  wife.  Professor  J.  T.  Wilson 
has  been  repeatedly  helpful  to  me  on  anatomical  points,  and  in  the 
Zoological  Laboratory  I  was  always  sure  of  obtaining  expert  advice  from 
Mr  James  Gray,  Mr  J.  T.  Saunders,  Mr  C.  F.  A.  Pantin  and  Dr  Eastham. 
I  have  relied  much  upon  the  kindness  and  wide  biological  knowledge  of 
Dr  D.  Keilin  and  Dr  F.  H.  A.  Marshall.  As  regards  the  historical  chapters, 
I  am  most  grateful  to  Dr  Charles  Singer,  who  annotated  them  with 
valuable  comments,  and  to  Professor  R.  C.  Punnett  who  placed  un- 
reservedly at  my  disposal  his  knowledge  of  the  history  of  generation,  and 
his  library  of  old  and  rare  biological  books.  To  Dr  Arthur  Peck  I  am 
indebted  for  the  correction  of  my  Greek,  and  it  was  Professor  A.  B.  Cook 
who  guided  me  to  the  embryology  of  the  ancients.  Without  the  assiduous 
backing  of  Mr  Powell,  the  Librarian  of  the  Royal  Society  of  Medicine,  and 
his  assistants,  I  should  have  dealt  much  more  inadequately  than  I  have 
with  the  papers  which  cannot  be  consulted  in  Cambridge.  I  have  also  to 
thank  the  administrators  of  the  Thruston  Fund  of  Gonville  and  Caius 
College  for  a  grant  which  was  devoted  to  incidental  expenses.  For  the 
indexes  I  wish  to  thank  Miss  Helen  Moyle,  and  for  other  services  which 
have  made  the  book  possible,  Mrs  V.  Townsend.  My  thanks  are  also 
due  to  the  Editors  of  the  following  journals:  Biochemical  Journal,  Journal 


of  Experimental  Biology,  Biological  Reviews,  Science  Progress,  and  the  Monist, 
for  permission  to  reprint  passages  from  papers.  I  must  record  my  gratitude 
to  the  following  friends,  who  very  kindly  read  through  and  criticised  the 
proofs  of  the  various  sections: 

Part  I 

Professor  A.  E.  Boycott 
Dr  J.  H.  Woodger 

Part  II 

Professor  R.  C.  Punnett 
Dr  Charles  Singer 
Dr  Reuben  Levy 
Dr  Arthur  Peck 
Sir  William  Dampier 
Professor  A.  B.  Cook 
The  Rev.  W.  Elmslie 
Professor  F.  M.  Cornford 

Part  III 


1  Professor  R.  H.  A.  Plimmer 
Mr  J.  B.  S.  Haldane 

2  Dr  Samuel  Brody 
Mr  James  Gray 
Dr  E.  N.  Willmer 

3  Mr  G.  R.  de  Beer 

Mr  C.  H.  Waddington 
Mr  J.  B.  S.  Haldane 

4  Dr  D.  Keilin 
Professor  Munro  Fox 

5  Mr  T.  R.  Parsons 
Dr  Malcolm  Dixon 

6  M.  Louis  Rapkine 
Mr  C.  Forster  Cooper 

7  Miss  Marjory  Stephenson 
M.  Louis  Rapkine 

Dr  D.  Keilin 

8  Dr  Eric  Holmes 

Dr  Bruce  Anderson  &  Mrs  Margaret 
Whetham  Anderson 




Dr  Dorothy  Jordan  Lloyd 

Professor  J.  Murray  Luck 

Mr  C.  Forster  Cooper 


Mile  Eliane  LeBreton 


Professor  J.  B.  Leathes 


Dr  Irvine  Page 


Dr  Elsie  Watchorn 


Dr  Barnet  Woolf 

MrJ.  B.  S.  Haldane 


Dr  Howard  Florey 


Dr  Leslie  J.  Harris 

Dr  A.  L.  Bacharach 


Dr  Howard  Whittle 


Mr  C.  F.  A.  Pantin 

Professor  A.  R.  Moore  &  Mrs  Moore 


Dr  John  Hammond 


Dr  St  G.  Huggett 


Dr  Arthur  Walton 


Dr  Barbara  Holmes 


Dr  F.  H.  A.  Marshall 


Professor  L.  G.  M.  B.  Becking 

Dr  D.  Keilin 

Dr  G.  S.  Carter 

Professor  Lancelot  Hogben 

Mr  G.  R.  de  Beer 

Professor  A.  R.  Moore  &  Mrs  Moore 

Appendix  III 
Dr  L.  E.  S.  Eastham 

I  am  indebted  to  the  Master  of  Gonville  and  Caius  College  for  permission 
to  reproduce  the  portrait  of  William  Harvey  (attributed  to  Rembrandt) 
in  the  Senior  Combination  Room.  Finally,  I  am  glad  to  record  here  my 
gratitude  to  the  StafTof  the  Cambridge  University  Press  for  the  unremitting 
care  which  they  gave  to  my  book  during  the  course  of  its  preparation. 

J.  N. 

Note:  The  use  of  the  shortened 
and  (&)  indicates  collaboration 
between  two  or  more  authors. 


The  Sciences,  unlike  the  Graces  or  the  Eumenides,  are  not  limited 
in  number.  Once  born,  they  are  immortal,  but,  as  knowledge  in- 
creases, they  are  ever  multiplying,  and  so  great  is  now  the  dominion 
of  the  scientific  mind  that  every  few  years  sees  a  new  one  brought 
into  the  world.  Some  spring,  fully  armed,  from  the  brains  of  one  or 
two  men  of  genius,  but  most  of  them,  perhaps,  come  only  gradually 
to  their  full  development  through  the  labours  of  very  many  obscure 
and  accurate  observers. 

If  the  analogy  may  be  permitted,  physico-chemical  embryology  has 
so  far  been  living  an  intra-uterine  existence.  Its  facts  have  been 
buried  in  a  wide  range  of  scientific  journals,  and  its  theories  have 
lain  dormant  or  in  potentia  in  reviews  of  modest  scope.  Physico- 
chemical  embryology  has,  indeed,  arrived  at  the  stage  immediately 
priox  to  birth,  and  all  it  needs  is  a  skilful  obstetrician,  for,  when  once 
it  has  reached  the  light  of  day  and  has  passed  for  ever  out  of  the 
foetal  stage,  it  will  be  well  able  to  take  care  of  itself.  This  obstetrical 
task  is  that  which  I  have  chosen  and  obviously  enough  it  divides 
into  three  principal  heads:  first,  to  collect  together  out  of  all  the 
original  papers  on  the  subject  the  facts  which  are  known  about  the 
physico-chemical  basis  of  embryonic  development;  second,  to  relate 
these  facts  to  each  other  and  to  the  facts  derived  from  the  labours 
of  investigators  in  morphological  embryology  and  "  Entwicklungs- 
mechanik,"  and,  third,  to  ascertain  whether,  from  what  is  at  present 
known,  any  generally  valid  principles  emerge. 

I  may  as  well  say  at  the  outset  that  in  order  to  do  this  certain 
arbitrary  boundary-lines  are  inevitable.  The  following  arrangement 
has  been  adopted.  Chronologically  speaking,  the  prelude  to  all  em- 
bryonic development  is  the  maturation  of  the  egg-cell,  but  this  is  not 
strictly  embryology,  and  so  has  been  relegated  to  an  appendix.  The 
egg-cell  as  a  physico-chemical  system  is  dealt  with  at  the  opening 
of  Part  III,  and  thereafter  the  physico-chemical  aspects  of  develop- 
ment follow  in  order.  No  mention  will  be  made  of  fertilisation,  for 
this  has  been  treated  exhaustively  by  other  writers  (Lillie,  Dalcq) 
and,  after  all,  embryology  presupposes  fertiUsation  whether  natural 
or  artificial.    Nor  in  later  chapters  will  any  complete  treatment  be 


given  of  the  events  going  on  in  the  maternal  organism  during  preg- 
nancy :  for  the  present  purpose  the  discussion  will  go  as  far  into  the 
mother  as  the  placenta  but  no  farther.  Again,  hatching  or  birth  will 
put  an  end  to  the  discourse  as  to  the  foetal  state  itself,  save  that,  in 
the  cases  of  animals  which  hatch  before  the  yolk-sac  is  absorbed, 
their  embryonic  life  is  assumed  to  end  when  they  first  take  food  for 
themselves.  Appendices  are  added  dealing  with  the  plant  embryo 
and  the  insect  pupa,  which,  in  the  later  stages  of  metamorphosis, 
have  points  both  of  resemblance  to  and  of  difference  from  the  growth 
of  the  embryo.  It  is  natural  to  hope  that  the  outcome  of  all  this  labour 
may  be  an  increase  of  interest  among  biologists  in  this  section  of  their 
domain,  and  a  great  accession  to  the  number  of  those  investigators 
who  devote  their  energies  to  actual  experiments  in  this  new  field. 

For  it  must  be  confessed  that  it  is  a  new  field.  It  has  been  opened 
up  in  very  gradual  stages:  fitful  and  sporadic  experiments  on  the 
constitution  of  embryonic  tissues  in  the  seventeenth  century,  a  gradual 
growth  of  knowledge  about  the  chemical  composition  of  eggs  in  the 
eighteenth,  a  big  increase  of  activity  in  the  early  nineteenth;  d'lTxiug 
which  appear  the  first  observations  on  the  physico-chemical  changes 
taking  place  in  the  embryo  during  its  development,  and  then  in  our 
own  time  a  mass  of  very  widely  scattered  work  bringing  the  subject 
up  to  the  "obstetrical"  stage.  Such  a  work  as  this,  in  my  opinion, 
should  not  be  compared  with  laboratory  experiments  in  a  derogatory 
sense,  for,  while  it  is  true  that  facts  are  the  ultimate  court  of  appeal 
in  any  scientific  discussion,  yet  at  the  same  time  the  number  of  in- 
vestigators has  grown  to  such  extraordinary  proportions  in  this  century 
that  some  danger  exists  lest  we  should  be  so  busily  engaged  in  accu- 
mulating new  facts  as  to  be  left  with  no  time  at  all  to  devote  any 
thought  to  those  we  have  already.  Classification,  indexing,  and 
maturer  consideration  about  the  facts  we  actually  possess  are  at  least 
as  great  a  need  at  the  present  moment  as  the  invention  of  new  facts. 
"Everyone  must  realise",  says  Eugenio  Rignano,  "how  much  this 
theoretical  elaboration,  performed  by  means  of  analyses  and  com- 
parisons, of  generalisations  and  hypotheses  controlled  and  verified  by 
the  correspondence  of  facts  with  the  results  of  the  reasoning,  is  useful 
and  necessary  if  one  wishes  to  reach  a  progressive  systematisation  and 
an  ever  more  synthetic  vision  of  the  confused  mass  of  facts  which 
experimentalists  pour  daily  in  a  continuous  stream  into  the  scientific 


My  predecessors  in  this  work  have  been  few  in  number.  The  volumes 
of  Haller's,  Buffon's,  and  Milne-Edwards'  great  treatises,  in  which 
they  deal  with  the  phenomena  of  generation,  contain  as  much  in- 
formation as  was  available  up  to  1863,  but  this  is  purely  of  historical 
interest  to  us.  In  1885,  W.  Preyer,  Professor  of  Physiology  at  Jena, 
published  his  Spezielle  Physiologie  des  Embryo,  which  still  remains  a  most 
valuable  review,  and  indeed,  even  to-day,  is  the  only  existing  book 
specially  devoted  to  embryonic  physiology.  The  present  century 
has  produced  only  three  books  which  even  touch  upon  my  subject, 
namely,  T.  B.  Robertson's  Chemical  Basis  of  Growth  and  Senescence, 
F.  H.  A.  Marshall's  Physiology  of  Reproduction  and  E.  Faure-Fremiet's 
La  Cinetique  du  Developpement.  The  first  of  these  was  admittedly  written 
to  support  a  particular  theory,  and  in  any  case  says  comparatively 
little  about  physico-chemical  embryology.  The  second  and  the  third 
deal  with  it  only  as  a  constituent  part  of  a  much  wider  field.  In 
Marshall's  case,  the  whole  array  of  facts  relating  to  oestrus  and 
breeding,  fertilisation  and  fertility,  lactation  and  sex  determination, 
have  to  be  dealt  with,  and  only  three  chapters  out  of  sixteen  are 
devoted  to  the  subject  of  this  book.  The  first  of  these  is  contributed 
by  W.  Cramer,  and  covers  the  biochemistry  of  the  sexual  organs,  in- 
cluding the  unfertiUsed  egg ;  the  second,  which  deals  with  foetal 
nutrition  and  the  placenta,  is  by  J.  Lochhead ;  and  the  third,  by  these 
two  investigators  together,  is  concerned  with  changes  in  the  maternal 
organism  during  pregnancy.  Admirable  as  these  chapters  are,  they 
are  now  rather  out  of  date.  Moreover,  though  one  or  two  corners 
of  the  field  I  have  before  me  were  covered  in  Marshall's  book,  it  was 
from  a  quite  different  standpoint. 

Faure-Fremiet's  work  is  exactly  analogous;  it  deals  with  physico- 
chemical  embryology  only,  as  it  were,  in  passing.  The  relevant  dis- 
cussion takes  up  only  two  chapters  out  of  seven ;  the  rest  are  occupied 
with  tissue  culture,  growth  of  protozoal  populations,  and  general 
cytology.  His  book  covers,  it  might  be  said,  the  third  and  fourth 
corners :  all  the  main  expanse  of  the  field  remains. 

Thus  neither  of  these  books  deals  with  physico-chemical  embryo- 
logy in  an  exhaustive  and  comprehensive  fashion,  treating  it  as,  in 
my  view,  it  ought  to  be  treated,  with  the  thoroughness  which  is 
deserved  by  a  new  branch  of  natural  knowledge.  Inseparable,  how- 
ever, from  thoroughness  of  treatment  is  the  submergence  of  the  parts 
of  more  general  interest  under  a  mass  of  detail,  and  it  may  be  well. 


therefore,  to  mention  now  what  sections  of  the  book  could  be  said 
to  be  most  valuable  to  any  student  of  general  biology.  Part  i  comes 
in  this  class,  and  of  Part  iii,  the  middle  portion  of  Section  i,  all  of 
Sections  2,  3,  and  5,  thelatter  half  of  Section  7,  Sections  8,  9  (especially 
the  end),  11,  possibly  18,  and  finally  the  Epilegomena. 

For  my  models  in  the  preparation  of  this  book,  if  it  is  permissible 
to  name  them,  I  have  taken,  Growth  and  Form  by  d'Arcy  Thompson, 
surely  the  most  scholarly  work  produced  by  a  biologist  in  our  time, 
and  The  Physiology  of  Reproduction  by  F.  H.  A.  Marshall,  already 
mentioned,  which  showed  to  all  successors,  in  my  opinion,  how  a 
colossal  array  of  facts  can  be  welded  together  into  an  absorbing  and 
readable  book,  I  am  conscious  that  I  shall  not  attain  the  level  of 
these  classics  of  modern  biology,  but  then 

....  Pauci,  quos  aequus  amavit 
Jupiter,  aut  ardens  evexit  ad  aethera  virtus. 

The  progress  of  any  branch  of  natural  knowledge  can  be  best 
described  as  a  continual  pilgrimage  towards  the  quantitative.  QuaUties 
can  never  be  altogether  left  out  of  account  and  this  is  what  makes 
it  impossible  for  science  to  achieve  its  end  with  absolute  finality.  Yet 
an  association  with  the  probably  unattainable  is  common  to  all  the 
great  types  of  man's  activity.  But  "Fuyez  toujours  les  a  peu  pres", 
as  O.  W.  Holmes  used  to  put  it,  is  a  proper  maxim  for  the  scientific 
mind,  and  whatever  this  book  can  do  towards  making  embryology 
an  exact  science  will  be  its  final  justification. 





.  .  .  .to  measure  all  things  that  can  be  measured,  and  to 
make  measurable  what  cannot  yet  be  measured. 


THE  THEORY  OF  ^^^-^S^aj^, 


Philosophy,  Embryology,  and  Chemistry 

The  penetration  of  physico-chemical  concepts  into  embryology 
has  not  been  entirely  peaceful.  "In  experimental  embryology",  it 
has  been  said,  "concepts  borrowed  from  the  physical  sciences  do  not 
admit  of  calculations  being  made,  and  until  they  do  they  are  not 
really  playing  the  same  role  as  they  do  in  the  sciences  from  which 
they  have  been  borrowed  and  for  which  they  were  devised."  "Nothing 
is  more  clear",  says  another  writer,  "in  chemistry  and  physics  than 
that  identical  results  follow  upon  identical  causes.  Introduce  a  dis- 
turbing element,  even  a  small  one,  into  your  experiment,  and  the 
experiment  will  fail.  Such  is  not  the  case  with  the  developing  egg." 
W.  McDougall,  too,  endows  the  egg  with  good  intentions.  "The 
embryo",  he  says,  "seems  to  be  resolved  to  acquire  a  certain  form 
and  structure,  and  to  be  capable  of  overcoming  very  great  obstacles 
placed  in  its  path.  The  development  of  the  forms  of  organisms  seems 
to  be  utterly  refractory  to  explanation  by  mechanical  or  physico- 
chemical  principles."  Finally,  J.  A.  Thomson  goes  farther  than  them 
all,  and  does  not  hesitate  to  say,  "It  is  a  mere  impious  opinion  that 
development  will  one  day  be  described  in  terms  of  mechanics". 
Chapter  iv  of  his  Gifford  Lectures  illustrates  the  antagonistic  attitude 
to  physico-chemical  embryology  in  its  most  acute  form. 

It  can  hardly  be  a  coincidence  that  so  many  among  the  great 
embryologists  of  the  past  were  men  of  strongly  philosophic  minds. 
It  would  be  absurd  to  support  this  opinion  by  citing  Aristotle,  but 
it  holds  less  obviously  true  of  William  Harvey,  whose  book  on  genera- 
tion is  full  of  thoughts  about  causation,  and  in  the  cases  of  Ernst 
von  Baer,  Ernst  Haeckel,  Wilhelm  Roux,  Hans  Driesch,  dArcy 
Thompson  and  J.  W.  Jenkinson,  there  is  no  doubt  about  it.  It  is  not 
really  surprising,  for  of  all  the  strange  things  in  biology  surely  the 
most  striking  of  all  is  the  transmutation  inside  the  developing  egg, 
when  in  three  weeks  the  white  and  the  yolk  give  place  to  che  animal 
with  its  tissues  and  organs,  its  batteries  of  enzymes  and  its  dehcately 
regulated  endocrine  system.  This  coming-to-be  can  hardly  have  failed 

8  THE  THEORY  OF  [pt. 

to  lead,  in  the  minds  of  those  most  intimately  acquainted  with  it,  to 
thoughts  of  a  metaphysical  character.  Nor,  it  seemed,  did  those  who 
worked  on  it  do  much  to  diminish  its  wonder.  "Neither  the  schools 
of  physicians",  as  Harvey  said,  "nor  Aristotle's  discerning  brain, 
have  disclosed  the  manner  how  the  Cock  and  its  seed,  doth  mint  and 
coine,  the  chicken  out  of  the  Ggg,'^  Or,  in  the  words  of  Erycius 
Puteanus,  "I  will  neglect  gold,  and  will  praise  what  is  more  precious 
than  any  metal,  I  will  despise  feasts,  and  will  set  forth  praises  of 
something  better  than  any  food  or  drink.  If  you  would  know  of  what 
it  is  that  I  intend  to  speak,  it  is  the  egg;  men  marvel  at  the  sun,  at 
meteors  flung  from  heaven,  at  stars  swimming  therein,  but  this  is 
the  greatest  of  all  wonders".  Here,  however,  there  is  one  significant 
thing.  It  is  that  the  very  chapter  of  Harvey's  book  in  which  the 
preceding  remark  is  found  has  as  its  heading  "The  Efficient  Cause 
of  the  Chicken,  is  hard  to  be  found  out".  It  certainly  was,  but  the 
right  clue  was  in  the  heading  to  that  exercitation. 

This  close  association  of  embryology  with  philosophy,  then,  made 
it  necessary  to  discuss  at  the  outset  of  this  book  certain  points  in  the 
more  theoretical  regions  of  biology,  and,  as  it  were,  to  defend  from 
a  theoretical  angle  the  extension  of  the  domain  of  physics  and 
chemistry  over  embryology.  I  might  have  entitled  this  part  of  the 
book  "The  philosophy  of  embryology",  but,  in  deference  to  those 
metaphysicians  who  rightly  insist  that  the  word  philosophy  should 
only  be  used  of  a  definite  system  of  experience  which  looks  at  the 
universe  as  a  corporate  whole,  I  adopted  the  present  heading.  Under 
it  I  propose  to  discuss  the  exact  status  of  the  chemical  aspect  of 
embryology.  For  many  biologists,  having  perhaps  insufficiently  con- 
sidered the  nature  of  the  scientific  method,  think  it  likely  that 
the  discoveries  of  modern  times  may  allow  of  some  other  basis  for 
biology  than  mathematical  physics  and  that  the  scientific  niethod 
may  rightly  be  different  in  biology  from  what  it  is  in  chemistry.  It 
is  this  factor  in  our  present  intellectual  climate  which  makes  it  neces- 
sary to  preface  by  a  philosophical  discussion  a  book  in  which  the 
concepts  of  physics  and  chemistry  are  extended  to  a  field  of  biology 
where  they  have  never  before  received  more  than  a  conventional  and 
formal  reverence. 

The  aim  of  all  studies  in  physico-chemical  embryology  must  be 
that  expressed  by  T.  H.  Huxley  when  he  said,  "  Zoological  Physiology 
is  the  doctrine  of  the  functions  or  actions  of  animals.    It  regards 


animal  bodies  as  machines  impelled  by  certain  forces  and  perform- 
ing an  amount  of  work  which  can  be  measured  and  expressed 
in  terms  of  the  ordinary  forces  of  nature.  The  final  object  of 
physiology  is  to  deduce  the  facts  of  morphology  on  the  one  hand 
and  those  of  oecology  on  the  other  hand  from  the  laws  of  the  mole- 
cular forces  of  matter".  It  may  be  regarded  as  very  noteworthy 
that  Huxley  here  puts  morphology  as  secondary  to  physiology  and 
as  it  were  derivable  from  it;  he  does  not  place  morphology  and 
physiology  on  two  high  places,  "neither  afore  or  after  other",  as 
has  so  often  been  done,  but  he  plainly  states  his  view  that  the 
anatomical  aspect  of  animals,  their  external  and  internal  forms,  could 
be  deduced  from  the  interplay  of  physico-chemical  forces  within 
them,  if  we  only  knew  enough  about  those  forces.  This  is  the  idea 
of  the  primacy  of  function.  It  seems  always  to  have  two  meanings, 
firstly,  the  Epicurean-Lucretian  one  which  Huxley  adopts  here  and 
Roux  so  brilliantly  developed,  in  which  shape  is  regarded  as  the 
outward  and  visible  sign  of  the  properties  of  matter  itself,  and, 
secondly,  the  Aristotelian  one  emphasised  by  J.  B.  de  Lamarck's 
writings  in  the  eighteenth  century,  and  in  our  time  by  E.  S.  Russell's 
great  work  Form  and  Function,  in  which  psychical  factors  are  intro- 
duced as  the  essential  elements  in  the  ultimate  analysis  of  shape.  In 
both  these  interpretations,  function  has  the  priority  over  form,  but 
the  meaning  of  function  is  the  point  of  difference.  Some  biologists, 
however,  seem  to  think  that  physiology  and  morphology  are  cate- 
gorical, and  the  latter  is  emphatically  not  reducible  to  or  derivable 
from  the  former.  The  two  spheres  of  study  represent,  for  them, 
correlative  and  immiscible  disciplines,  morphology  aiming  ultimately 
at  solid  geometry,  physiology  at  causation,  and  "rerum  cognoscere 
causas"  is  not  the  basic  desire  of  the  scientific  mind.  They  object 
to  the  view  which  regards  "the  ovum  as  a  kind  of  chemical  device 
wound  up  and  ready  to  go  off  on  receipt  of  a  stimulus,  the  task  of 
the  causal  morphologist  being  to  disentangle  the  complex  of  events 
which  constitute  the  unwinding  process"  (Woodger),  complaining 
that  in  this  view  no  account  is  taken  of  the  past  history  of  the 
race,  which  is  left  to  genetics,  again  a  causal  discipHne.  To  some 
extent  these  opinions  spring  from  a  conviction  that  the  analytical 
method  is  inapplicable  to  a  living  being  because  it  is  an  organism,  and 
of  that  there  is  more  to  be  said.  But  they  also  arise  from  a  profound 
unwillingness  to  subsume  biology  under  physics  and  a  desire  to  uphold 

10  THE  THEORY  OF  [pt. 

"the  autonomy  of  biology".  This  precludes  the  promise  of  an  ever- 
increasing  homogeneity  in  the  structure  of  science,  and  hence  an 
ever-increasing  simplicity. 

The  Historical  Perspective 

That  the  older  embryologists  awaited  the  extension  of  physico- 
chemical  conceptions  to  embryology  is  no  mere  matter  of  conjecture. 
Until  the  mechanical  theory  of  the  universe  had  been  consolidated 
by  the  " corpuscularian  philosophy"  of  the  seventeenth  century  it 
would  be  useless  to  look  for  illustration  of  this,  but  by  1674  John 
Mayow  was  tracing  the  part  played  by  the  " nitro-aerial  particles" 
in  the  development  of  the  embryo,  and  in  1732  Hermann  Boerhaave 
was  discussing  chemical  problems  with  explicit  reference  to  embryonic 
development.  Many  other  examples  of  this  point  of  view  in  the 
eighteenth  century  will  be  given  later.  Then,  when  the  second  decade 
of  the  nineteenth  century  had  nearly  gone,  von  Baer,  perhaps  the 
greatest  of  all  embryologists,  was  careful  to  preface  his  Entwicklungs- 
geschichte  by  a  careful  account  of  all  that  was  known  about  the 
chemical  constitution  of  the  Qgg,  and  that,  although  his  philosophical 
inclinations  were  deeply  vitalistic,  and  even  his  practical  interests 
morphological.  In  Roux,  of  course,  this  future  reference  came  out 
explicitly,  and  the  extension  of  biochemistry  into  embryology  was 
allowed  for  and  foreseen.  An  early  instance  was  the  association  be- 
tween Wilhelm  His  and  Hans  Miescher.  Miescher,  writing  to  Hoppe- 
Seyler  in  1872  said,  "I  am  now  collecting  material  from  fishes, 
birds,  and  amphibia  to  lead  to  a  chemical  statics  of  development. 
With  this  end  in  view  I  shall  do  analyses  of  ash,  nuclein,  and  lecithin". 

Embryology  before  Harvey,  however,  was  rigidly  Aristotelian,  a 
statement  the  meaning  of  which  George  Santayana  has  lucidly  ex- 
plained. "Aristotle",  said  he,  "distinguished  four  principles  in  the 
understanding  of  Nature.  The  ignorant  think  that  these  are  all, 
equally,  forces  producing  change,  and  the  cooperative  sources  of  all 
natural  things.  Thus,  if  a  chicken  is  hatched,  they  say  that  the  Efficient 
Cause  is  the  warmth  of  the  brooding  hen,  yet  this  heat  would  not 
have  hatched  a  chicken  out  of  a  stone,  so  that  a  second  condition, 
which  they  call  the  Material  Cause,  must  be  invoked  as  well,  namely, 
the  nature  of  an  egg;  the  essence  of  eggness  being  precisely  a  capacity 
to  be  hatched  when  warmed  gently — because,  as  they  wisely  observe, 
boiling  would  drive  away  all  potentiality  of  hatching.    Yet,  as  they 


further  remark,  gentle  heat-in-general  joined  with  the  essence-of- 
eggness  would  produce  only  hatching-as-such  and  not  the  hatching 
of  a  chicken,  so  that  a  third  influence,  which  they  call  the  Final 
Cause,  or  the  End-in-view,  must  operate  as  well,  and  this  guiding 
influence  is  the  divine  idea  of  a  perfect  cock  or  a  perfect  hen  presiding 
over  the  incubation  and  causing  the  mere  eggness  in  the  egg  to 
assume  the  likeness  of  the  animals  from  which  it  came.  Nor,  finally, 
do  they  find  that  these  three  influences  are  sufficient  to  produce  here 
and  now  this  particular  chicken,  but  are  compelled  to  add  a  fourth, 
a  Formal  Cause,  namely,  a  particular  yolk,  a  particular  shell,  and 
a  particular  farmyard,  on  which  and  in  which  the  other  three  causes 
may  work,  and  laboriously  hatch  an  individual  chicken,  probably 
lame  and  ridiculous  despite  so  many  sponsors."  The  Aristotelian 
account  of  causation  could  not  be  better  expressed.  Santayana  puts 
this  description  of  it  into  the  mouth  of  Avicenna  in  his  imaginary 
dialogue,  and  makes  him  go  on  to  say,  "Thus  these  learned  babblers 
would  put  nature  together  out  of  words,  and  would  regard  the  four 
principles  of  interpretation  as  forces  mutually  supplementary  com- 
bining to  produce  material  things ;  as  if  perfection  could  be  one  of 
the  sources  of  imperfection  or  as  if  the  form  which  things  happen 
to  have  could  be  one  of  the  causes  of  their  having  it.  Far  differently 
do  these  four  principles  clarify  the  world  when  discretion  conceives 
them  as  four  rays  shed  by  the  light  of  an  observing  spirit".  In  this 
last  observation  we  may  perhaps  trace  the  germ  of  the  Copernican 
revolution  in  philosophy  effected  by  Kant,  if  we  may  take  it  to  enclose 
the  idea  of  the  activity  of  the  experient  subject  in  all  perception. 

In  science  generally,  however,  the  x\ristotelian  conceptions  went 
without  serious  contradiction,  and  thus  formed  the  framework  for  all 
the  embryological  work  that  was  done,  as,  for  instance,  by  Albertus 
Magnus.  Owing  to  its  association  with  the  idea  of  the  plan  of  a 
divine  being,  the  final  cause  tended  in  the  Middle  Ages  to  eclipse 
the  others.  In  the  seventeenth  century  this  feeling  is  well  shown  in 
a  remarkable  passage,  which  occurs  in  the  Religio  Medici  of  Sir  Thomas 
Browne:  "There  is  but  one  first  cause,  and  four  second  causes  of  all 
things;  some  are  without  Efficient,  as  God;  others  without  Matter,  as 
Angels;  some  without  Form,  as  the  first  matter;  but  every  Essence 
created  or  uncreated,  hath  its  Final  cause,  and  some  positive  End  both 
of  its  Essence  and  Operation ;  this  is  the  cause  I  grope  after  in  the 
works  of  Nature ;  on  this  hangs  the  providence  of  God ;  to  raise  so 

12  THE  THEORY  OF  [pt. 

beauteous  a  structure  as  the  World  and  the  Creatures  thereof,  was 
but  his  Art;  but  their  sundry  and  divided  operations,  with  their 
predestinated  ends,  are  from  the  Treasure  of  his  Wisdom.  In  the 
causes,  nature,  and  affections  of  the  EcHpses  of  the  Sun  and  Moon 
there  is  most  excellent  speculation,  but  to  profound  farther,  and  to 
contemplate  a  reason  why  his  providence  hath  so  disposed  and 
ordered  their  motions  in  that  vast  circle  as  to  conjoyn  and  obscure 
each  other,  is  a  sweeter  piece  of  Reason  and  a  diviner  point  of 
Philosophy;  therefore  sometimes,  and  in  some  things,  there  appears 
to  me  as  much  Divinity  in  Galen  his  books  De  Usu  Partium,  as  in 
Suarez'  Metaphysicks:  Had  Aristotle  been  as  curious  in  the  enquiry 
of  this  cause  as  he  was  of  the  other,  he  had  not  left  behind  him  an 
imperfect  piece  of  Philosophy  but  an  absolute  tract  of  Divinity". 
This  was  written  in  Harvey's  time,  and  in  Harvey's  thought  the  four 
causes  were  still  supreme ;  his  De  Generatione  Animalium  is  deeply  con- 
cerned with  the  unravelling  of  the  causes  which  must  collaborate  in 
producing  the  finished  embryo.  But  the  end  of  their  domination  was 
at  hand,  and  the  exsuccous  Lord  Chancellor,  whose  writings  Harvey 
thought  so  little  of,  was  making  an  attack  on  one  of  Aristotle's  causes 
which  was  destined  to  be  peculiarly  successful.  There  is  no  need  to 
quote  his  immortal  passages  about  the  "impertinence",  or  ir- 
relevance, of  final  causes  in  science,  for  they  cannot  but  be  familiar 
to  all  scientific  men.  Bacon  demonstrated  that  from  a  scientific  point 
of  view  the  final  cause  was  a  useless  conception;  recourse  to  it  as  an 
explanation  of  any  phenomenon  might  be  of  value  in  metaphysics, 
but  was  pernicious  in  science,  since  it  closed  the  way  at  once  for 
further  experiments.  To  say  that  embryonic  development  took  the 
course  it  did  because  the  process  was  drawn  on  by  a  pulling  force, 
by  the  idea  of  the  perfect  adult  animal,  might  be  an  explanation  of 
interest  to  the  metaphysician,  but  as  it  could  lead  to  no  fresh  experi- 
ments, it  was  nothing  but  a  nuisance  to  the  man  of  science.  Later 
on,  it  became  clear  also  that  the  final  cause  was  irrelevant  in  science 
owing  to  its  inexpressibility  in  terms  of  measurable  entities.  From 
these  blows  the  final  cause  never  recovered.  In  England  the  seven- 
teenth century  was  the  time  of  transition  in  these  aflfairs,  and  in  such 
books  as  Josfeph  Glanville's  Plus  Ultra  and  Scepsis  Scientifica,  for  in- 
stance, and  Thomas  Sprat's  Defence  of  the  Royal  Society,  the  stormy 
conflict  between  the  "new  or  experimental  philosophy"  and  the 
Aristotelian  "school-philosophy"  can  be  easily  followed.    Francis 


Gotch  has  given  a  delightful  account  of  the  evening  of  AristoteUanism, 
but  it  involved  a  stormy  sunset,  and  the  older  ideas  did  not  give 
way  without  a  struggle.  Harvey's  work  is  perfectly  representative  of 
the  period  of  transition,  for,  in  his  preface  under  the  heading  "Of  the 
Method  to  be  observed  in  the  knowledge  of  Generation",  he  says, 
"Every  inquisition  is  to  be  derived  from  its  Causes,  and  chiefly  from 
the  Material  and  Efficient".  As  for  the  formal  cause.  Bacon  expressly 
excluded  it  from  Physic,  and  it  quietly  disappeared  as  men  saw  that 
scientific  laws  depended  on  the  repeatableness  of  phenomena,  and 
that  anything  unique  or  individual  stood  outside  the  scope  of  science. 
Thus  in  the  case  of  the  developing  egg,  the  formal  (the  particular 
farmyard,  etc.)  and  the  final  causes  are  scientifically  meaningless, 
and  if  it  were  desired  to  express  modern  scientific  explanation  in 
Aristotelian  terminology,  the  material  and  efficient  causes  would 
alone  be  spoken  of,  essence-of-eggness  being  a  "chymical  matter" 
as  well  as  the  heat  of  the  brooding  hen. 

Obstacles  to  Chemical  Embryology 

The  complexity  of  living  systems,  however,  is  such  that  many 
minds  find  it  difficult  to  accept  this  physico-chemical  account  as  the 
most  truly  scientific  way  of  looking  at  it.  This  is  doubtless  due  in  part 
to  an  erroneous  notion,  which  is  yet  very  tenacious  of  existence,  that 
the  mechanical  theory  of  the  universe  must,  if  accepted  at  all,  be 
accepted  as  an  ultimate  ontological  doctrine,  and  so  involve  its  sup- 
porter in  one  of  the  classical  varieties  of  metaphysical  materialism. 
It  cannot  be  too  strongly  asserted  that  this  is  not  the  case.  To  imagine 
that  it  is,  is  to  take  no  account  of  the  great  space  that  separates  us 
from  the  last  century.  "When  the  first  mathematical,  logical,  and 
natural  uniformities",  said  WilHam  James,  "the  first  Laws,  were 
discovered,  men  were  so  carried  away  by  the  clearness,  beauty,  and 
simplification  that  resulted  that  they  believed  themselves  to  have 
deciphered  authentically  the  eternal  thoughts  of  the  Almighty.  His 
mind  also  thundered  and  reverberated  in  syllogisms.  He  also  thought 
in  conic  sections,  squares,  and  roots  and  ratios,  and  geometrised  like 
Euclid.  He  made  Kepler's  laws  for  the  planets  to  follow,  he  made 
velocity  increase  proportionately  to  the  time  in  falhng  bodies;  he 
made  the  laws  of  the  sines  for  light  to  obey  when  refracted;  he 
established  the  classes,  orders,  families,  and  genera  of  plants  and 
animals,  and  fixed  the  distances  between  them." 

14  THE  THEORY  OF  [pt. 

Far  different  is  the  account  of  itself  which  science  has  since  learned 
to  give.  But  this  change  of  attitude  is  not  a  revolt  against  thought 
as  such,  or  against  reason  as  such ;  it  is  only  a  loss  of  belief  in  the 
literal  inspiration  of  the  formulae  proper  to  science.  It  would  be  just 
as  extravagant  to  claim  that  the  scientific  investigator  of  the  twentieth 
century  sets  down  absolute  truths  in  his  laboratory  notebook,  and, 
armed  with  an  infallible  method,  explores  the  real  structure  of  an 
objective  world,  as  it  would  be  fantastic  to  claim  that  Jehovah 
dictated  an  absolute  code  of  the  good  to  Moses  on  Mount  Sinai.  To 
say  that  the  development  of  a  living  being  can  best  be  described  in  a 
metrical  or  mechanical  way  is  not  to  say  that  it  is  metrical  or  me- 
chanical and  nothing  else.  The  physico-chemical  embryologist  is  not 
committed  to  any  opinion  on  what  his  material  really  is,  but  he  is 
committed  to  the  opinion  that  the  scientific  method  is  one  way  of 
describing  it,  and  that  it  is  best  to  apply  that  method  in  its  full  rigour 
if  it  is  to  be  applied  at  all.  In  other  words,  following  the  train  of 
thought  of  William  James,  he  does  not  assert  that  the  courts  of  Heaven 
as  well  as  those  of  our  laboratories  resound  with  expressions  such  as 
"organisers  of  the  second  grade,"  and  "so  many  milHgrams  per  cent." 
The  mechanical  theory  of  the  world,  which  is,  as  many  beHeve, 
bound  up  indissolubly  with  one  of  the  ultimate  types  of  human 
experience,  can  no  longer  be  considered  as  necessarily  involving  the 
exclusion  of  other  theories  of  the  world.  Or,  put  in  another  way,  it 
is  a  theory  of  the  world,  and  not  a  pocket  edition  of  the  world  itself 

But  before  bringing  forward  any  arguments  in  support  of  this 
attitude  and  in  defence  of  physico-chemical  embryology,  it  will  be 
well  to  consider  briefly  those  theoretical  tendencies  in  modern  biology 
which  go  together  under  the  inexact  adjective  "neo-vitalistic",  for 
their  influence  in  scientific  thought  has  been  far-reaching.  To  deal 
critically  with  them  is  not  a  waste  of  time,  for,  were  we  to  adopt 
any  one  of  them,  we  should  find  that  the  notion  of  embryology  as 
complicated  biophysics  and  biochemistry  would  have  to  be  abandoned, 
and  quite  other  means  of  approach  (never,  indeed,  very  well  defined) 
would  have  to  be  used. 

The  Stumbling-block  of  Hormism 

Hormism,  or  "Psychobiology,"  may  be  dealt  with  in  a  few 
words.  Chiefly  supported  by  A.  Wagner  in  Germany,  and  by 
E.  S.  Russell  and  L.  T.  Hobhouse  in  this  country,  it  holds  that — to 


use  Lloyd  Morgan's  terminology — a  physiological  tale  cannot  be  told 
separately  from  a  psychological  tale.  Instead  of  expressing  living 
processes  in  terms  of  physical  causes  and  effects,  the  hormists  wish 
to  regard  unconscious  striving  as  the  essential  urge  in  life,  and  such 
conceptions  as  food,  rest,  fatigue,  etc.,  as  irreducible  biological  cate- 
gories. These  thinkers  do  not  often  acknowledge  their  debt  to  Galen 
of  Pergamos,  who  put  forward,  as  early  as  a.d.  170,  an  essentially 
similar  conception  as  the  basis  of  his  biology.  In  the  treatise  On  the 
Natural  Faculties  he  says,  "The  cause  of  an  activity  I  term  a  faculty.... 
Thus  we  say  that  there  exists  in  the  veins  a  blood-making  faculty, 
as  also  a  digestive  faculty  in  the  stomach,  a  pulsatile  faculty  in  the 
heart,  and  in  each  of  the  other  parts  a  special  faculty  corresponding 
to  the  function  or  activity  of  that  part".  He  also  said,  "We  call  it 
a  faculty  so  long  as  we  are  ignorant  of  the  cause  which  is  operating", 
but  he  never  actually  suggested  any  such  underlying  cause,  and 
seems  to  have  thought  it  impossible  to  ascertain.  So  do  the  hormists. 
According  to  them  the  actions  of  protozoa  are  to  be  described  in 
terms  of  avoiding  responses,  seeking  responses  and  the  like,  language 
which,  as  they  claim,  is  much  simpler  than  the  complex  terminology 
of  surface  tension  and  molecular  orientation.  Everything,  of  course, 
depends  on  what  is  meant  by  simple.  To  say  that  a  protozoon  seeks 
the  light  is  evidently  more  naive  than  to  say  that  a  dimolecular 
photochemical  reaction  takes  place  in  its  protoplasm  leading  to  an 
increase  of  lactic  acid  or  what  not  on  the  stimulated  side,  but  since 
the  latter  explanation  fits  into  the  body  of  scientific  fact  known 
already  it  is  open  to  the  biochemist  to  say  that,  for  his  part,  he.  con- 
siders the  latter  explanation  the  simpler.  It  is,  in  fact,  simpler  in 
the  long  run.  Psychobiology  or  hormism  differs  from  the  other 
forms  of  neo-vitalism  because  it  insists  on  retaining  "  commonsense  " 
explanations  in  biology  as  categories  of  biological  thought  beneath 
which  it  is  impossible  to  go.  It  dismisses  the  entelechy  of  dynamic 
Teleology,  on  the  ground  that  it  acts,  as  it  were,  in  addition  to  the 
mechanistic  schema,  accepting  the  latter  fully  but  interfering  in  it. 
It  resembles  much  more  finaUsm  and  organicism,  but  lays  stress 
rather  on  the  unconscious  striving  force  which  seems  to  animate 
colloidal  solutions  of  carbohydrates,  fats,  and  proteins.  It  resembles 
the  Behaviourism  of  J.  B.  Watson  superficially  by  emphasising  animal 
behaviour,  but  it  fundamentally  differs,  for  it  asks  the  question — Does 
an  animal  see  the  green  light  and  the  red  light  in  this  experiment 

i6  THE  THEORY  OF  [pt. 

as  we  do,  or  does  it  see  them  as  two  shades  of  grey  as  colour-blind 
people  do?  while  the  behaviourist  asks — Does  it  respond  according 
to  difference  of  light-intensity  or  difference  of  wave-lengths  ?  Hormism, 
in  fact,  recurs  continually  to  psychical  factors.  Samuel  Butler,  for 
instance,  one  of  its  principal  exponents,  wrote,  "I  want  to  connect 
the  actual  manufacture  of  the  things  a  chicken  makes  inside  an  egg 
with  the  desire  and  memory  of  the  chicken  so  as  to  show  that  one 
and  the  same  set  of  vibrations  at  once  change  the  universal  sub- 
stratum into  the  particular  phase  of  it  required"  (cf.  ^  rov  hwdixei, 
6vTo<i  ivreXex^ta  fj  tolovtov)  "and  awaken  a  consciousness  of  and  a 
memory  of  and  a  desire  towards  this  particular  phase  on  the  part  of 
the  molecules  which  are  being  vibrated  into  it".  "The  Hormist 
contends",  says  Lloyd  Morgan,  "that  something  which  is  very 
difficult  to  distinguish  from  a  '  plan-in-mind '  on  the  part  of  the 
embryo  chick  or  rabbit  does  freely  determine  the  course  of  events 
in  specific  growth  from  egg  to  adult.  This,  I  urge,  is  a  metaphysical 
hypothesis  which  goes  beyond  biology  or  psychology  as  branches  of 

Finalism  as  a  Rock  of  Offence 

Finalism  and  dynamic  Teleology  are  closely  connected,  for  both 
of  them  embody  an  attempt  to  go  back  to  the  Aristotelian  inclusion  of 
the  final  cause  as  an  integral  essential  of  scientific  explanation,  and 
to  regard  the  Baconian  attitude  to  teleology  as  a  mistake.  They  solve 
Kant's  antinomy  of  the  teleological  judgment  simply  by  deleting  the 
proposition,  and  leaving  the  counter-proposition.  They  are  weakest 
on  their  practical  side,  for  their  supporters  do  not  suggest  any  altera- 
tions which  might  be  made  in  scientific  method,  although  their 
fundamental  assumptions  plainly  require  it.  The  principal  repre- 
sentative of  finalism  is  Eugenio  Rignano,  and  dynamic  teleology 
has  been  for  the  most  part  upheld  by  Hans  Driesch. 

Rignano,  in  his  Qii' est-ce-que  la  Vie?  and  his  Biological  Memory  has 
contended  that,  though  the  mechanical  concept  of  the  universe  may 
be  perfectly  satisfactory  as  a  description  of  the  world  of  physics,  yet 
animals  and  plants  show  so  much  purposiveness  that  mechanical 
categories  are  absolutely  inadequate  for  them.  Biology,  therefore, 
cannot  be  complicated  physics  and  chemistry,  but  must  be  something 
sui  generis  and  with  its  own  methods  and  laws.  "The  long  debate 
between  vitalists  and  mechanists,"  he  says,  "in  attempting  to  give 


an  explanation  of  life,  cannot  lead  to  any  conclusion  unless  that 
fundamental  characteristic  common  to  all  vital  phenomena  of  pre- 
senting a  purposive,  teleological,  or  finaUstic  aspect  in  their  most 
typical  manifestations  is  first  thoroughly  examined."  The  most  suc- 
cinct account  of  his  views  and  of  the  exact  biologist's  answer  to  them  will 
be  found  in  his  Man  Not  a  Machine,  and  in  the  volume  Man  a  Machine 
in  the  same  series.  The  way  in  which  they  affect  embryology  is 
significant,  and  may  be  found  in  his  chapter  called  "Finalism  of  the 
generative  and  regenerative  phenomena".  "Even  if",  he  says,  "the 
organism  could  be  explained  as  a  physico-chemical  machine,  there 
would  still  remain  to  be  explained  the  most  fundamental  thing — how 
the  machine  constructed  itself  The  purposiveness  of  the  ontogenetic 
development  is  too  evident  to  be  denied.  It  results  from  the  con- 
vergence of  manifold  morphogenetic  activities  to  one  sole  end,  that 
is,  to  the  formation  of  a  marvellous  functional  unity,  every  part  of 
which  serves  to  maintain  the  life  and  guarantee  the  well-being  of  the 
whole.  The  embryo  in  its  development  manifests  at  every  stage  a 
'  harmony  of  composition '  as  Driesch  calls  it,  which  has  a  touch  of 
the  marvellous ;  parts  and  elements  of  an  organ  develop  independently, 
but  when  they  have  finished  their  development  they  are  found  to 
fit  together  perfectly  like  the  parts  of  a  machine  and  the  one  so 
answers  to  the  other  that  they  unitedly  form  one  complex  organ. 
Thus  the  mouth  and  intestine  of  the  sea-urchin  begin  their  develop- 
ment at  two  points  distant  from  each  other  and  develop  indepen- 
dently, but  as  they  grow  the  one  moves  towards  the  other,  so  that 
when  development  is  ended  they  fit  together  perfectly  and  form  a 
single  canal."  This  passage  illustrates  the  line  of  argument  found 
throughout  Rignano,  and  I  will  not  remark  on  it  further  than  to 
draw  attention  to  the  mention  of  the  marvellous  in  it,  another  hint, 
if  any  were  needed,  of  that  strain  of  misplaced  "numinous  instinct" 
which  seems  to  be  present  in  all  biological  vitaHsts.  Omnia  exeunt 
in  mysterium  would  seem  to  be  "a  discouraging  maxim"  for  the 
scientific  worker.  "The  direction",  Rignano  goes  on  to  say,  "of 
ontogenetic  development  toward  a  predetermined  end  is  also  in- 
fluenced by  the  fact  that  the  embryo  overcomes  early  disturbances 
which  might  deflect  it  from  its  course.  Ontogenesis  thus  seems  to  be 
marshalled  by  some  occult  intelligence  or  entelechy  in  the  same  way 
that  the  construction  of  a  machine  and  the  direction  of  its  work  is 
presided  over  by  the  mind  of  the  engineer." 

i8  THE  THEORY  OF  [pt. 

Rignano's  arguments  are  open  to  grave  objection  on  two  main 
grounds,  first,  that  he  regards  biology  as  suffering  more  than  physics 
from  the  teleology  of  things,  and,  second,  that  he  wishes  to  bring  the 
concept  of  purposiveness  back  into  natural  science. 

The  first  of  these  is  inadmissible  both  on  philosophic  and  scientific 
grounds.  Bernard  Bosanquet  best  expresses  the  former  attitude.  He 
was  led  to  his  conclusions  by  the  conviction  that  James  Ward  and 
other  opponents  of  scientific  naturalism  had  gone  too  far  in  their 
polemics  against  the  mechanical  theory  of  the  universe,  and  had 
rested  the  case  for  teleology  only  "on  the  capacity  of  the  finite 
consciousness  for  guidance  and  selection".  This  he  considered  a 
mistake.  "Things  are  not  teleological",  he  said,  "because  they  are 
de  facto  purposed  but  necessary  to  be  purposed  because  they  are 
teleological.,.. The  foundations  of  teleology  in  the  universe  are  far 
too  deeply  laid  to  be  accounted  for  by,  still  less  restricted  to,  the 
intervention  of  finite  consciousness.  Everything  goes  to  show  that 
such  consciousness  should  not  be  regarded  as  the  source  of  teleology 
but  as  itself  a  manifestation  falling  within  wider  manifestations  of 
the  immanent  individuality  of  the  real."  Bosanquet  proceeds,  fol- 
lowing out  the  thought  of  his  teacher,  Lotze,  "The  contrast,  then, 
of  mechanism  with  teleology,  is  not  to  be  treated  as  if  elucidated 
at  one  blow  by  the  antithesis  of  purposive  consciousness  and  the 
reactions  of  part  on  part.  It  is  rooted  in  the  very  nature  of  totality, 
which  is  regarded  from  two  complementary  points  of  view,  as  an 
individual  whole,  and  as  constituted  of  interacting  members".  But 
Rignano's  arguments  are  unsatisfactory  also  from  a  scientific  angle, 
and  here  the  objection  comes  from  Lawrence  J.  Henderson,  whose 
book  The  Fitness  of  the  Environment,  probably  the  most  important 
contribution  to  biological  thought  in  this  century,  is  never  referred  to 
by  Rignano.  It  cannot  now  be  necessary  to  recount  how  Henderson 
examined  the  question  of  the  finality  of  our  present  scientific  know- 
ledge, and,  judging  that  it  was  considerable,  went  on  to  enquire  into 
the  properties  of  the  elements  and  compounds  principally  associated 
with  life.  His  conclusion  was  that  living  animals  and  plants  exist  in 
an  environment  just  as  fitted  for  them  as  they  are  for  it,  that  the 
Darwinian  concept  of  fitness  works,  indeed,  both  ways,  and  that 
there  is  a  reciprocity  between  organism  and  environment  so  that 
every  teleological  action  done  by  an  individual  organism  bears  upon 
it  the  image  and   superscription  of  universal  teleology.  Thus  the 


conclusion  of  the  thought  of  Bosanquet  and  Henderson  was  that, 
though  teleology  was  a  conception  which  it  was  impossible  to 
do  without,  yet  any  limitation  of  it  to,  or  special  association  of  it 
with,  living  organisms,  was  inadmissible.  The  question  remained, 
What  has  teleology  to  do  with  science? 

This  point  has  been  approached  best  by  J.  W.  Jenkinson  with  his 
usual  clarity.  "Those  who  uphold  teleological  doctrine",  he  said, 
"seem  to  have  fallen  into  a  confusion  between  two  different  things, 
the  formal  and  the  final  cause.  The  material,  efficient,  and  formal 
causes,  if  we  mean  by  the  last  the  idea  of  the  effect  in  the  mind  of  a 
sentient  being,  all  precede  in  time  the  occurrence  of  the  effect;  and 
this  kind  of  teleology  is  not,  as  it  is  asserted  to  be,  a  doctrine  of  final, 
but  one  of  formal  causes.  The  final  cause  stands  for  the  use  to  which 
an  object  is  to  be  put,  the  effect  it  will  produce,  the  function  it  will 
perform,  which  obviously  succeed  in  time  the  existence  of  the  object 
itself  The  final  cause,  then,  cannot  be  taken  as  ever  determining  in 
time  the  existence  of  the  object  itself,  and  is  therefore  a  conception 
which  belongs  not  to  science  but  to  metaphysics.  The  only  necessary 
conditions  of  a  phenomenon  ascertainable  by  science  are  those 
material  and  efficient  causes  which  precede  it."  Or,  as  Streeter  puts 
it,  "If  there  is  purpose  in  nature,  we  ought  not  to  expect  science  to 
reveal  it.  Purpose  is  activity,  the  direction  of  which  is  determined 
by  an  end,  that  is,  by  an  apprehension  of  quality  or  value.  But 
quaUty  cannot  be  measured,  and  therefore  from  its  essential  nature 
it — and  along  with  it  purpose — lies  outside  the  sphere  of  science". 
Or,  finally,  to  go  straight  to  the  fountain-head,  "If  I  say",  says 
Kant,  "that  I  must  judge  according  to  merely  mechanical  laws  of 
the  possibility  of  all  events  in  material  nature  and  consequently  of  all 
forms  regarded  as  its  products,  I  do  not  therefore  say:  they  are 
possible  in  this  way  alone.  All  that  is  impUed  is:  I  must  always 
reflect  on  them  according  to  the  principle  of  the  mere  mechanism 
of  nature  and  consequently  investigate  this  as  far  as  I  can ;  because 
unless  this  Ues  at  the  basis  of  investigation  there  can  be  no  proper 
knowledge  of  nature  at  all".  Purposiveness,  in  fact,  is  not  a  concep- 
tion which  interlocks  with  quantitative  treatment;  that  mathematical 
expression  of  relationships  which  is  the  ideal  type  of  all  science 
has  here  nothing  upon  which  to  impinge,  and  the  pulling  force, 
perpetually  going  on  before,  eludes  and  must  always  elude,  if  this 
analysis  is  correct,  the  advancing  web  of  mechanical  explanation. 

20  THE  THEORY  OF  [pt. 

If,  then,  Bacon  and  his  successors  were  right  in  banishing  the 
concept  of  teleology  from  scientific  thought,  the  physico-chemical 
embryologist  need  not  be  alarmed  by  the  finalism  with  which, 
according  to  Rignano,  the  whole  of  ontogenetic  development  is  suf- 
fused. In  fact,  it  is  not  the  phenomenon,  but  only  one  way  of  looking 
at  it,  that  is  finalistic,  and  it  is  this  aspect  of  it  that  must  be  neglected 
in  scientific  work  if  the  gravest  confusion  is  to  be  avoided.  Is  there 
need  for  the  biologist  to  be  any  more  afraid  of  the  Drieschian  en- 
telechy  (Aristotle's  eVreXe^em  Actuality)  making  what  might  be  into 
what  is  and  directing  from  within  the  development  of  the  embryo  in 
the  egg  or  the  uterus?  The  word  "entelechy"  as  used  by  Aristotle 
meant  that  which  exists  in  the  highest  sense  of  the  word,  whether 
actually  or  potentially,  e.g.  the  sword  in  the  mind  of  the  swordmaker 
before  a  single  one  of  the  necessary  operations  of  manufacture  had 
been  begun.  The  entelechy  therefore  operated  on  the  process  in 
question  by  means  of  the  final  cause,  and  did  not  reside  in  the 
changing  entity  if  it  was  dead  like  the  sword,  though  it  did  if  it  was 
alive  like  the  embryo.  Driesch  frequently  says  that  he  uses  the  word 
in  a  quite  different  sense  from  Aristotle,  but  the  majority  of  his 
readers  find  it  impossible  to  discover  any  essential  point  of  divergence. 
He  does  at  any  rate  make  it  much  more  precise  than  Aristotle,  for  he 
defines  it  as  a  non-spatial  element  in  the  living  being,  which  at  one 
time  suspends  possible  action  and  at  another  time  relaxes  such 
suspension,  acting  in  this  way  as  the  bearer  of  "individualising 
causality"  and  bringing  the  animal  from  potentiality  into  actuality. 

It  seems  that  this  inherent  immanent  formative  power  has  been 
translated  by  biologists  of  every  period  since  Aristotle  into  the  lan- 
guage of  their  time.  Just  as  Driesch  now  tries  to  acclimatise  it  to  the 
unfavourable  environment  of  a  post-Cartesian  world,  so  St  Gregory  of 
Nyssa,  who  lived  about  a.d.  370,  clothed  it  in  patristic  terminology, 
and  produced  a  theological  variety  of  neo-vitalism.  His  most  im- 
portant biological  works,  the  irepl  KaraaKevrjq  dvdpcoirov,  On  the  making 
of  Man,  and  Trepl  '^v^V'^i  On  the  Soul,  contained  such  passages  as  these, 
"The  thing  so  implanted  by  the  male  in  the  female  is  fashioned 
into  the  different  varieties  of  limbs  and  interior  organs,  not  by  the 
importation  of  any  other  power  from  without,  but  by  the  power 
which  resides  in  it  transforming  it".  And  elsewhere,  "For  just  as  a 
man  when  perfectly  developed  has  a  soul  of  a  specific  nature,  so  at 
the  fount  and  origin  of  his  life,  he  shows  in  himself  that  conformation 


of  soul  which  is  suitable  for  his  need  in  its  preparing  for  itself  its 
peculiarly  fit  dwelling-place  by  means  of  the  matter  implanted  in 
the  maternal  body,  for  we  do  not  suppose  it  possible  that  the  soul  is 
adapted  to  a  strange  building,  just  as  it  is  not  possible  that  a  certain 
seal  should  agree  with  a  different  impression  made  in  wax". 

Thus  the  soul  makes  its  body  as  if  it  were  a  gem  making  a  stamp 
upon  some  soft  substance,  and  acting  during  embryogeny  from 
within — a  conception  essentially  like  that  of  Driesch.  We  shall  see 
later  how  many  Renaissance  authors  adopted  similar  views,  e.g. 
Fienus.  "No  unsouled  thing",  says  Gregory,  "has  the  power  to 
move  and  to  grow.  Yet  there  is  no  doubt  that  the  embryo  moves 
and  waxes  big  as  it  is  fed  in  the  body  of  the  mother."  There  is  nothing 
new  about  dynamic  teleology;  it  is  by  no  means  the  outcome  of 
newly  ascertained  facts :  it  recurs  from  time  to  time  in  the  history  of 
biological  thought  because  it  is  the  natural  result  of  an  unscientific 

I  do  not  propose  to  discuss  here  the  facts  which  originally  led 
Driesch  to  the  views  expressed  in  his  Science  and  Philosophy  of  the 
Organism,  for  they  are  very  well  known,  and  have  been  shown  by 
J.  W.  Jenkinson,  H.  S.  Jennings,  H.  C.  Warren  and  A.  E.  Boveri, 
among  others,  to  be  interpretable  on  quite  other  lines.  Nor  shall  I 
demonstrate  by  a  comparison  of  passages  from  Driesch  and  Paracelsus 
how  closely  the  conception  of  immanent  formative  force  or  entelechy 
approaches  the  master-archaeus  of  Paracelsus  and  the  later  iatro- 
chemists  such  as  Stahl,  for  Driesch  has  done  it  himself  in  his  History 
and  Theory  of  Vitalism.  The  inference  from  it  is  that  the  Drieschian 
entelechy  has  been  and  will  be  of  no  more  use  as  a  practical  working 
hypothesis  for  the  laboratory  than  the  archaeus  was  in  the  past. 

Driesch's  dynamic  teleology  is  open  to  more  serious  and  funda- 
mental objections.  These  were  not  obvious  at  the  first  appearance 
of  his  Gifford  Lectures,  but  were  clearly  brought  to  light  through 
the  controversy  which  Jacques  Loeb  had  with  H.  S.  Jennings  and 
which  resulted  in  the  publication  of  their  respective  books,  Forced 
Movements,  Tropisms,  and  Animal  Conduct  and  The  Behaviour  of  the  Lower 
Organisms.  Loeb's  theory  of  tropisms  entirely  dispensed  with  any 
psychological  factors,  but  Jennings  upheld  the  view  that  they  might 
be  legitimately  brought  under  scientific  discussion,  provided  they 
were  regarded  as  being  determined  as  well  as  determining.  This  led 
him  to  make  a  new  enquiry  into  scientific  methodology,  and  he 

22  THE  THEORY  OF  [pt. 

published  his  results  in  a  valuable  series  of  papers  from  1911  to  191 8. 
He  concluded  that  the  pursuance  of  laboratory  work  demands  as  its 
minimum  of  system  what  he  called  "Radical  Experimental  Deter- 
minism", and  that  there  was  difference  of  opinion  as  to  whether 
this  might  regard  conscious  or  unconscious  mental  processes  as  links 
in  the  chain  of  determinate  causation.  On  this  point  Jennings  and 
Loeb  were  antagonists,  but  both  were  united  against  Driesch,  from 
whose  writings  it  now  appeared  that  psychical  events  might  or  might 
not  affect  physical  events  according  to  circumstances,  and  that  the 
entelechy  was  subject  to  no  general  laws.  Neal  had  maintained  that 
the  experimentally  discoverable  perceptual  determiners  in  living 
things  were  insufficient  to  account  for  the  effects  produced  in  them. 
Jennings  pointed  out  that,  if  this  meant  that  the  non-perceptual 
(mental)  determiners  acted  supplementarily  to  the  others  and  not 
instead  of  them,  it  was  compatible  with  radical  experimental  deter- 
minism. But,  if  it  was  said  that  some  of  the  determiners  were  non- 
perceptual  and  could  not  be  known  at  all,  then  it  was  incompatible. 
Now  it  was  just  this  that  Driesch  had  been  saying.  "A  complete 
knowledge",  he  wrote,  "of  all  physico-chemical  things  and  relations 
(including  possible  relations)  of  a  given  system  at  a  time  t  would 
not  give  a  complete  characterisation  of  that  system  if  it  is  a  living 
system. .  .  .  Practically  we  may  say  that  complete  knowledge  of  the 
physico-chemical  constitution  of  a  given  egg  in  a  given  state  and  of 
the  behaviour  following  this  constitution  in  one  case,  implies  the 
same  knowledge  for  other  cases  (in  the  same  species)  with  great 
probability.  But  this  is  a  probability  in  principle  and  can  never  be 
more.  It  would  not  even  be  a  probability  if  we  did  not  know  the 
origin  of  a  given  egg  in  a  given  state,  i.e.  that  the  egg  was  the  tgg, 
say,  of  an  ascidian.  But  to  know  this  history  or  origin,  is  of  course, 
already  more  than  simply  to  know  its  physico-chemical  constitution 
and  its  consequences  in  one  case,  which  suffices  in  the  realm  of  the 
inorganic.  It  may  be  that  the  eggs  of  echinoidea,  fishes,  and  birds, 
are  the  same  in  all  the  essentials  of  physico-chemical  constitution. 
Something  very  different  happens  in  each  case  on  account  of  the 
different  entelechies.  In  spite  of  this  we  know  with  great  probability 
what  will  happen  from  one  case  if  we  know  that  this  egg  comes 
from  a  bird  and  that  from  an  echinoid.  Therefore,  practically,  ex- 
perimental indeterminism  is  not  a  great  danger  for  science." 

But  the  matter  was  taken  up  by  various  writers,  and  Lovejoy, 


especially,  defended  Driesch  from  the  charge  of  interfering  with  the 
fundamental  necessities  of  scientific  thought.  Jennings,  however, 
was  able  to  publish  in  reply  letters  from  Driesch  in  which  these 
implications  of  his  position  were  fully  admitted.  "Two  systems  abso- 
lutely identical  in  every  physico-chemical  respect  may  behave  differ- 
ently under  absolutely  identical  conditions  if  the  systems  are  living 
systems.  For  the  specificity  of  a  certain  entelechy  is  among  the 
complete  characteristics  of  a  living  organism  and  about  this  entelechy 
knowledge  of  physico-chemical  things  and  relations  teaches  abso- 
lutely nothing."  Such  a  basis  for  experimental  work  was  generally 
felt  to  carry  with  it  its  own  condemnation. 

It  is  interesting  to  recall,  in  this  connection,  the  vivid  account 

given  by  Claude  Bernard  of  the  polemic  he  had  with  Gerdy  at 

the  Philomathic  Society  in  Paris,  for  the  Driesch-Lovejoy-Jennings 

controversy    simply    repeated    on    a    larger   scale    the    arguments 

of  the   two    Parisian    biologists    sixty   years    before.     "In    1859," 

says    Claude    Bernard,    "I    made    a    report    to    the    Philomathic 

Society    in    which    I    discussed    the    experiments    of  Brodie    and 

Magendie  on  ligature  of  the  bile-duct,  and  I  showed  that  the  divergent 

results  which  the  two  experimentalists  reached  depended  on  the  fact 

that  one  operated  only  on  dogs  and  tied  only  the  bile-duct,  while 

the  other  operated  only  on  cats,  and,  without  suspecting  it,  included 

in  his  ligature  both  the  bile-duct  and  a  pancreatic  duct.  Thus  I 

explained  the  difference  in  the  results  they  reached  and  concluded 

that  in  physiology  as  everywhere  else  experiments  are  rigorous  and 

give  identical  results  wherever  we  operate  in  exactly  similar  Conditions. 

A  propos  of  this  a  member  of  the  Society  took  the  floor  to  attack  my 

conclusions ;  it  was  Gerdy,  a  surgeon  at  the  Charite,  professor  in  the 

faculty  of  medicine  and  known  through  various  works  in  surgery 

and  physiology.  'Your  anatomical  explanation  of  these  experiments', 

said  he,  'is  correct,  but  I  cannot  accept  your  general  conclusions. 

You  say,  in  fact,  that  the  results  of  experiments  in  physiology  are 

identical;  I  deny  it.    Your  conclusion  would  be  correct  for  inert 

nature  but  cannot  be  true  for  living  nature.  Whenever  life  enters 

into  phenomena',  he  went  on,  'conditions  may  be  as  similar  as  we 

please,  the  results  may  still  be  different.'  To  support  his  opinion  Gerdy 

cited  cases  of  individuals  with  the  same  disease,  to  whom  he  had 

given  the  same  drugs  with  different  results.    He  also  recalled  cases 

of  like  operations  for  the  same  disease,  but  followed  by  cure  in  one 

24  THE  THEORY  OF  [pt. 

case  and  death  in  another.  These  differences,  according  to  him,  all 
depended  on  life  itself  altering  the  results,  though  the  experimental 
conditions  were  the  same,  but  this  could  not  happen,  he  thought, 
in  the  phenomena  of  inert  bodies,  where  life  does  not  enter.  Opposi- 
tion to  these  ideas  was  prompt  and  general  in  the  Philomathic 
Society.  Everyone  pointed  out  to  Gerdy  that  his  opinions  were 
nothing  less  than  a  denial  of  biological  science,  but  he  would  not 
give  up  his  ideas  and  entrenched  himself  behind  the  word  'vitality'. 
He  could  not  be  made  to  understand  that  it  was  only  a  word,  devoid 
of  meaning  and  corresponding  to  nothing,  and  that  saying  that  some- 
thing was  due  to  vitality  amounted  to  calling  it  unknown."  The 
only  difference  between  Driesch  and  Gerdy  seems  to  be  that  Driesch's 
arguments  rested  on  a  more  solid  basis  of  fact,  and  were  put  forward 
with  greater  eloquence. 

It  is  worth  while  to  study  the  thought  of  Claude  Bernard  more 
closely.  Bernard  was  so  subtle  a  thinker  that  it  has  always  been 
difficult  to  classify  him  with  any  of  the  main  currents  of  biological 
thought,  but  the  following  passage  seems  to  me  to  sum  up  as  well  as 
any  other  the  main  shape  of  his  ideas.  "When  a  chicken  develops  in 
an  egg",  said  he,  "the  formation  of  the  animal  body  as  a  grouping  of 
chemical  elements  is  not  what  essentially  distinguishes  the  vital  force. 
This  grouping  takes  place  only  according  to  laws  which  govern  the 
physico-chemical  properties  of  matter ;  but  the  guiding  idea  of  the 
vital  evolution  is  essentially  of  the  domain  of  life  and  belongs  neither 
to  chemistry  nor  to  physics  nor  to  anything  else.  In  every  living  germ  is 
a  creative  idea  which  develops  and  exhibits  itself  through  organisation. 
As  long  as  a  living  being  persists  it  remains  under  the  influence  of 
this  same  creative  vital  force,  and  death  comes  when  it  can  no  longer 
express  itself;  here,  as  everywhere,  everything  is  derived  from  the  idea 
which  alone  creates  and  guides ;  physico-chemical  means  of  expres- 
sion are  common  to  all  natural  phenomena  and  remain  mingled 
pell-mell,  like  the  letters  of  the  alphabet  in  a  box,  till  a  force  goes  to 
fetch  them  to  express  the  most  varied  thoughts  and  mechanisms.  This 
same  vital  idea  preserves  beings  by  reconstructing  the  vital  parts 
disorganised  by  exercise  or  destroyed  by  accident  or  disease.  To  the 
physico-chemical  conditions  of  this  primal  development,  then,  we 
must  always  refer  our  explanation  of  life,  whether  in  the  normal  or 
pathological  state."  Here  Bernard  seems  to  recognise  the  significance 
of  universal  teleology,  for  he  says,  "here,  as  everywhere,  everything 


is  derived,  etc.",  and  at  the  same  time  he  lays  stress  on  the  identifica- 
tion of  the  physico-chemical  aspect  with  the  scientific  aspect,  going 
on,  indeed,  to  say  that  "physiologists  can  only  act  indirectly  through 
animal  physico-chemistry,  i.e.  physics  and  chemistry  worked  out  in 
the  field  of  life,  where  the  necessary  conditions  of  all  living  organisms 
develop,  create,  and  support  each  other  according  to  a  definite  idea 
and  obedient  to  rigorous  determinism".  It  is  true  that  elsewhere  he 
identifies  this  "force  that  goes  to  arrange  the  letters  of  the  alphabet" 
with  the  "mediating  nature"  of  Hippocrates  and  the  archaeus 
faber  of  van  Helmont.  Had  he  read  more  in  Lucretius  than  in 
Aristotle,  he  might  rather  have  spoken  of  it  as  a  necessary  outcome 
of  the  constitution  of  nature,  a  suggestion  more  profoundly  in 
harmony,  perhaps,  with  the  natural  bent  of  the  scientific  conscious- 
ness (cf  Bacon's  remarks  on  Democritus  in  De  Augmentis  Scientiarum) . 
But,  even  so,  he  evidently  regards  it  as  the  subject-matter  of  meta- 
physics and  not  of  science,  for  he  says  in  the  next  paragraph,  "The 
term  'vital  properties'  is  only  provisional  because  we  call  properties 
'  vital '  which  we  have  not  yet  been  able  to  reduce  to  physico-chemical 
terms,  though  doubtless  we  shall  succeed  in  that  some  day". 

Organicism  as  an  Occasion  of  Falling 

By  making  use  of  the  thought  of  Bernard,  we  pass  by  an  imper- 
ceptible transition  from  finalism  and  dynamic  teleology  to  or- 
ganicism, another  of  the  principal  forms  which  the  opposition  to 
mechanistic  biology  has  taken.  This,  like  some  of  the  other  doctrines 
I  have  mentioned,  has  a  long  history  behind  it.  The  notion,  "We 
murder  to  dissect",  finds  clear  expression  as  early  as  a.d.  200,  when 
Q^.  Septimius  Tertullianus,  of  Carthage,  one  of  the  Western  Fathers, 
spoke  thus  of  Herophilus,  the  Alexandrian  anatomist,  "Herophilus, 
the  physician,  or  rather  butcher,  dissected  600  persons  that  he  might 
scrutinise  nature;  he  hated  man  that  he  might  gain  knowledge. 
I  know  not  whether  he  explored  clearly  all  the  internal  parts  of  man 
for  death  itself  changes  them  from  their  state  when  alive,  and  death 
in  his  hands  was  not  simply  death,  but  led  to  error  from  the  very  process 
of  cutting  up".  No  more  excellent  statement  of  the  organicistic  view- 
point could  be  devised.  Sir  Kenelm  Digby  in  1644  gave  a  still 
clearer  summary  of  this  point  of  view,  and  even  in  the  rationalistic 
eighteenth  century  there  were  scientific  men  who  objected  to  the 
use  of  the  term  machine-like  as  applied  to  animals,  and  insisted  that 

26  THE  THEORY  OF  [pt. 

the  living  being  was  an  organism.  Cuvier  took  a  very  definite  stand 
on  this  question  when  he  said,  "All  the  parts  of  a  body  are  inter- 
related, they  can  act  only  in  so  far  as  they  all  act  together;  trying 
to  separate  one  from  the  whole  means  transferring  it  to  the  realm 
of  dead  substance  and  entirely  changing  its  essence".  But  the  name 
most  familiarly  associated  with  biological  organicism  in  this  country 
is  that  of  J.  S.  Haldane,  who  has  frequently  set  forth  his  views  upon 
this  subject.  His  attitude  is  so  well  known  that  it  need  not  be  de- 
scribed here  at  any  length,  but,  in  brief,  he  points  out  that  the  living 
animal  is  an  entity  with  a  far  higher  degree  of  internal  relatedness 
than  any  non-living  system,  and  holds  that  the  organic  cannot 
be  understood  by  a  study  of  its  parts  though  the  inorganic  very 
possibly  can.  In  other  words,  an  organism  is  an  entity  whose  parts 
lose  all  their  characteristic  properties  when  they  are  studied  away 
from  the  organism  itself;  they  fall,  as  it  were,  into  meaninglessness 
as  soon  as  they  are  abstracted  from  the  whole  of  which  they  are 
parts.  Consequently  that  kind  of  physiology,  and  a  fortiori  biophysics 
and  biochemistry,  which  analyses  living  organisms,  is  insufficient 
as  an  apparatus  for  understanding  living  things  and  should  give 
place  to  studies  in  which  organisms  are  regarded  intact.  Moreover, 
it  is  only  in  the  untouched  organism  that  those  wonderfully  well- 
balanced  actions  are  seen  by  which  the  animal  or  plant  holds  to  its 
own  niche  in  the  economy  of  nature,  resisting  every  attempt  to  dis- 
lodge it,  provided  the  attempt  be  not  so  successful  as  to  disorganise  the 
living  thing.  This  power  of  maintaining  a  constancy  in  its  external  and 
internal  environment  is  what  Haldane  regards  as  the  deus  ex  machina,  the 
property  of  living  things  essentially  inexplicable  by  physico-chemical 
hypotheses  and  requiring  special  biological  language  for  its  formula- 
tion. (For  a  discussion  of  the  "inconceivability  argument"  in  bio- 
logy, see  Mackenzie  and  Needham.)  "All  attempts",  he  says,  "to 
trace  the  ultimate  mechanism  of  life  must  be  given  up  as  meaningless. 
The  aim  of  biology  becomes  a  very  different  one — to  trace  in 
increasing  detail,  and  with  increasing  clearness,  the  organic  deter- 
mination which  the  organic  conception  formulates."  It  is  to  be 
noted,  however,  that  Haldane  vigorously  criticised  Drieschian  neo- 
vitalism,  adducing  against  it  the  argument  of  impossibility  of  inter- 
ference with  the  second  law  of  thermo-dynamics,  and  the  dubiousness 
of  the  theory  of  guidance  without  work  done,  a  discussion  of  which 
on   much   better   foundations   was   subsequently   given   by   Lotka. 


Haldane  was  not  convincing  in  his  criticism  of  Driesch,  and  there 
can  be  little  doubt  that  Driesch's  position  is  a  perfectly  tenable  one, 
provided  its  supporter  closes  his  eyes  to  the  nature  of  the  scientific 
method  on  the  one  hand,  and  the  actual  history  of  recent  scientific 
progress  on  the  other.  Another  side  of  Haldane's  teaching  was  the 
view  that  the  living  animal  was  in  some  way  less  abstract  than  the 
world  of  physics ;  physics  and  biology,  he  thought,  might  some  day 
coalesce,  but  it  would  then  be  found  that  physics  would  not  have 
swallowed  up  biology;  rather  the  contrary  would  occur  and  biology 
would  swallow  up  physics.  "The  idea  of  life",  he  said,  "is  nearer 
to  reality  than  the  ideas  of  matter  and  energy,  and  therefore  the 
presupposition  of  ideal  biology  is  that  inorganic  can  ultimately  be 
resolved  into  organic  phenomena,  and  that  the  physical  world  is  thus 
only  the  appearance  of  a  deeper  reality  which  is  as  yet  hidden  from 
our  distinct  vision  and  can  only  be  seen  dimly  with  the  eye  of  scien- 
tific faith." 

There  had  been  precursory  voices  of  all  this  in  the  nineteenth 
century,  as  when,  in  spite  of  the  discoveries  of  Cagniard  de  Latour 
and  others  that  the  yeast-cell  played  an  essential  part  in  fermenta- 
tion, Justus  von  Liebig  refused  to  credit  them,  fearing  that  their 
suggestions  were  a  return  to  explanations  by  vital  force.  "Chemical 
actions  may  very  well  explain  physiological  actions,  but  certainly 
not  vice  versa  ",  said  Moritz  Traube.  Claude  Bernard,  moreover,  dis- 
cussed the  matter  with  his  usual  subtlety.  "Physiologists",  he  said, 
"must  not  forget  that  a  living  being  is  an  organism  with  its  own 
individuality.  Since  physicists  and  chemists  cannot  take  their  stand 
outside  the  universe  they  study  bodies  and  phenomena  in  themselves 
and  separately  without  necessarily  having  to  connect  them  with 
nature  as  a  whole.  Physiologists,  on  the  contrary,  find  themselves 
outside  the  animal  organism  which  they  see  as  a  whole,  even  when 
trying  to  get  inside  so  as  to  understand  the  mechanism  of  every  part. 
The  result  is  that  physicists  and  chemists  reject  all  idea  of  final  causes 
for  the  facts  which  they  observe  while  physiologists  are  inclined  to 
acknowledge  an  harmonious  and  pre-established  unity  in  an  organised 
body,  all  of  whose  actions  are  independent  and  mutually  generative. 
If  we  break  up  an  organism  for  the  sake  of  studying  its  parts  it  is  only 
for  the  sake  of  ease  in  experimental  analysis,  and  by  no  means  in 
order  to  conceive  them  separately.  Indeed,  when  we  wish  to  ascribe 
to  a  physiological  quality  its  value  and  true  significance  we  must 

28  THE  THEORY  OF  [pt. 

always  refer  it  to  this  whole  and  draw  our  final  conclusions  only  in 
relation  to  its  effect  on  the  whole.  It  is  doubtless  because  he  felt  this 
necessary  interdependence  among  the  parts  of  an  organism  that 
Cuvier  said  that  experimentation  was  not  applicable  to  living  beings 
since  it  separated  organised  parts  that  should  remain  united.  For 
the  same  reason  vitalists  proscribe  experiments  in  medicine.  These 
views,  which  have  their  correct  side,  are  nevertheless  false  in  their 
general  outcome  and  have  greatly  hampered  the  progress  of  science." 
Bernard  did  not  commit  himself  to  an  absolutely  unambiguous  state- 
ment as  to  the  correct  and  incorrect  sides  of  organicism,  and  seems  to 
have  regarded  it  as  true  only  in  the  sense  that  imaginative  synthesis 
must  follow  radical  experimental  analysis.  He  was  therefore  quite 
opposed  to  that  true  and  keen-edged  organicism  represented  by 
Cuvier  and  other  biologists,  which  denied  the  bare  utility  and 
legitimacy  of  the  experimental  analysis,  and  which  was  not  un- 
justly satirised  by  Woolf  in  1927: 

You  cannot  demonstrate  the  soul 

Except  upon  the  animal  as  a  whole; 

Spiritual  autolytic  changes  begin 

As  soon  as  you  push  a  needle  through  the  skin. 

Haldane's  writings  and  those  of  his  school,  such  as  J.  A.  Thomson 
and  G.  G.  Douglas,  had  extremely  little  effect  on  the  direction  taken 
by  biological  science  in  the  first  years  of  this  century.  As  A.  D. 
Ritchie  pointed  out,  it  is  extraordinarily  difficult  to  find  out  anything 
about  living  systems,  unless  their  parts  are  treated  in  isolation,  even 
if  that  be  recognised  as  but  the  preliminary  for  imaginative  synthesis, 
and,  as  many  observers  said,  Haldane's  own  researches  in  the  physio- 
logy of  breathing  afforded  an  excellent  example  of  the  usual  scientific 
method.  Biological  research  proceeded  steadily  on  the  usual  lines, 
for  Haldane's  practical  counsels  could  only  be  followed  by  those  who 
were  willing  to  abandon  causal  explanations  in  biology  or  to  give 
up  the  hope  of  biology  becoming  an  exact  science. 

An  influence  was  at  hand,  however,  which  was  to  lessen  very  much, 
if  not  to  destroy  altogether,  the  attraction  of  Haldane's  opinions  for 
biologists.  A.  N.  Whitehead  had  in  his  earlier  works,  The  Concept 
of  Mature  and  The  Principles  of  Natural  Knowledge,  elaborated  his  theory 
of  extensive  abstraction,  but  it  was  not  until  the  publication  of  his 
Science  and  the  Modern  World  that  it   began  to  exercise  any  wide- 


spread  effect  upon  scientific  men  other  than  mathematical  physicists. 
Whitehead  boldly  extended  the  concept  of  the  organism  to  cover  all 
objects,  i.e.  all  events,  non-living  as  well  as  living.  The  word  "in- 
organic" would  thus  cease  to  apply  to  non-living  nature  and  all 
physical  systems  would  be  regarded  as  in  a  sense  incomprehensible, 
except  when  regarded  as  wholes  composed  of  parts  owing  their  very 
existence  to  their  share  and  arrangement  in  the  whole  in  question. 
Quoting  Tennyson's,  '"The  stars',  she  whispers,  'blindly  run'",  he 
says,  "An  electron  within  a  living  body  is  different  from  an  electron 
outside  it,  by  reason  of  the  plan  of  the  body.  The  electron  blindly  runs 
within  or  without  the  body,  but  it  runs  within  the  body  in  accordance 
with  the  general  plan  of  the  body  and  this  plan  includes  the  mental 
state.  But  this  principle  of  modification  is  perfectly  general  throughout 
nature,  and  represents  no  property  peculiar  to  living  bodies". 

Lloyd  Morgan  recognised  in  Whitehead's  organisms  his  "systems 
of  relations  going  together  in  substantial  unity",  which  he  had  con- 
ceived of  as  stretching  in  degrees  of  ever  vaster  complexity  from  the 
smallest  physical  event  to  the  universe  itself.  It  was  Lloyd  Morgan, 
indeed,  who  pointed  out  first  the  significance  of  Whitehead's  argu- 
ments for  biological  thought.  He  showed  that  the  extension  of 
organicism  to  cover  the  entire  world  of  physics  had  no  serious  con- 
sequences for  biological  mechanists  (who  would  continue  to  employ 
physico-chemical  methods  as  before),  provided  that  they  had  not 
adopted  some  form  of  scientific  naturalism.  At  the  same  time,  it 
could  have  little  help  for  those  who  had  insisted  that  the  principal 
characteristic  of  living  things  was  their  organismic  character,  and 
had  been  led  by  this  to  propose  far-reaching  alterations  in  scientific 
logic  or  to  give  up  the  hope  of  causal  explanation  in  biology.  If, 
as  it  would  seem,  there  are  organisms  everywhere,  then  the  position 
that  there  are  organisms  nowhere  turns  out  to  be  better  placed  than 
the  position  that  living  things  are  organisms  and  not  other  things ; 
for,  in  the  former  case,  peace  can  be  at  once  secured  by  attention 
to  definitions,  while  in  the  latter  case  the  irreducible  characteristic 
of  life  is  not  organicism,  whatever  else  it  may  be.  The  difference 
between  the  living  and  the  non-living  becomes  a  quantitative  one, 
expressible  in  degrees  of  organisation.  As  has  been  pointed  out, 
Haldane's  prophetic  observations  concerning  the  eventual  meeting- 
place  of  physics  and  biology  have  perhaps  at  last  been  justified,  but, 
if  so,  with  a  barren  benefit  to  neo- vitalism. 

30  THE  THEORY  OF  [pt. 

Organicism  and  Emergence 

We  may  now  pass  by  another  small  transition,  from  organicism 
to  theories  of  emergence.  Neo- vitalism  in  this  form  practically  ceases 
to  have  any  claim  to  the  name,  and  approaches  extremely  closely 
to  neo-mechanism.  The  principle  of  emergence  in  its  simplest  form 
is  the  statement  that  there  are  levels  of  existence  in  the  universe,  at 
each  of  which  some  more  complicated  form  of  being  comes  into 
existence,  containing  some  essence  absolutely  new,  and  which  could 
not  have  been  predicted,  even  if  all  the  properties  of  the  constituents 
of  the  lower  order  had  been  known.  This  is  evidently  a  conception 
very  close  to  that  of  the  organism,  for  just  as  the  living  or  non-living 
system,  looked  at  from  one  point  of  view,  ceases  to  be  itself  as  soon 
as  it  is  dismembered,  so  the  new  level  of  complexity,  looked  at  from 
one  point  of  view,  consists  of  lower  levels  of  complexity  joined  together 
in  a  way  that  could  not  have  been  foreseen,  because  its  properties 
and  peculiarities  are  not  the  sum  of  the  properties  and  peculiarities 
of  its  constituents.  But  it  is  important  to  note  that  there  are  here  two 
parentheses,  namely,  "looked  at  from  one  point  of  view",  implying 
that  there  is  another  point  of  view,  and  though  the  discussion  is 
complicated  here  by  the  doubt  as  to  whether  Whitehead  intends  his 
organisms  to  be  taken  as  a  metaphysical  theory,  or  as  a  scientific 
theory,  yet  in  Lloyd  Morgan  the  statement  is  clear  that  the  emergent 
point  of  view  has  always  a  complementary  one,  the  resultant  point 
of  view,  "the  emergent  web  and  the  resultant  woof"  as  he  calls  it. 
This  is  really  a  new  and  more  accurate  way  of  putting  the  ancient 
antithesis  of  mechanism  and  teleology,  for  the  scientific  method  in- 
volves the  concept  of  resultance,  since  it  continually  seeks  for  the 
predetermining  causes  which  must  be  in  some  way  uniform  with 
their  effects,  while  the  advent  of  something  absolutely  new  at  each 
level,  i.e.  atom  to  molecule,  colloidal  aggregate  to  living  cell,  etc., 
is  a  speculation  hardly  germane  to  science  and  resembling  the  final 

We  find  ourselves  back  again,  then,  at  the  distinction  between 
metaphysics  and  science,  which  was  first  seriously  studied  by  Kant. 
Most  of  the  confusion  has  arisen  in  the  past  through  an  insufficiently 
clear  decision  as  to  the  nature  of  biology.  Biology  cannot  be  philo- 
sophical and  scientific,  emergent  and  resultant,  indeterminate  and 
determinate,  teleological  and  mechanical  at  one  and  the  same  time. 


No  doubt  the  most  powerful  solvent  of  vitalism  will  turn  out  to 
be  the  set  of  changes  now  taking  place  in  physics.  It  is  as  yet  too 
early  to  describe  very  definitely  the  effects  of  these,  and  several 
modern  writers  on  the  subject  are  rather  free  in  their  use  of  the  word 
"mysticism",  but  it  is  at  any  rate  clear  that  physicists  are  coming  to 
see  more  clearly  than  before  the  impHcations  and  the  limitations  of 
the  study  of  the  metrical  aspects  of  the  world,  which  is  what  science  is. 
Behind  these  sets  of  numbers  and  quantities  the  background  of  the 
world  is  enigmatic,  and  Heisenberg's  Principle  of  Indeterminacy 
indicates  that  extreme  accuracy  can  only  be  obtained  at  a  cost. 
Again,  the  abandonment  of  the  model  in  physics  is  a  highly  important 
step,  and  physics  seems  to  have  reached  a  point  at  which  there  is  no 
analogy  in  our  everyday  experience  for  the  phenomena  with  which 
it  is  dealing,  so  that  we  cannot  even  picture  in  ordinary  words  what 
is  happening.  Eddington,  in  his  great  work  The  Nature  of  the  Physical 
World,  also  shows  that  physics  no  longer  speaks  of  the  motion  of 
every  individual  particle  in  the  universe  being  rigidly  determined  but 
rather  of  the  relative  probabilities  of  its  motions,  i.e.  the  odds  on 
them.  If  this  funeral  of  Laplace's  Calculator  should  turn  out  to 
be  enduring,  a  good  deal  of  difficulty  may  vanish  from  the  biological 
sphere.  But  I  should  prefer  to  leave  the  working  out  of  these  possi- 
bilities to  those  better  qualified  than  myself,  and  to  suggest  simply 
that  if  the  mechanical  theory  of  the  world  is  being  reconstructed  by 
modern  physics,  there  may  be  a  widespread  sapping  of  the  force  of 
neo-vitaHstic  contentions  in  the  near  future.  I  have  often  thought 
that  neo-vitalists  were  thinkers  whose  religious  sense  had  got  into  the 
wrong  place;  unable  to  set  up  commonsense  watertight  compart- 
ments on  the  one  hand,  or  to  work  out  a  philosophy  of  the  forms  of 
experience  on  the  other,  they  brought  the  numinous  into  biology  and 
abused  biophysics.  The  fundamental  contention  of  the  mechanists 
always  was  that  science  and  the  scientific  method  were  one  and  that 
biology  was  complicated  physics — this  remains  unaltered.  But  if 
physics  is  more  and  more  obviously  throwing  off  the  links  which 
bound  it  in  the  past  to  metaphysical  materiahsm,  and  admitting 
itself  to  be  the  study  of  the  metrical  aspects  of  the  world,  there  will 
be  perhaps  less  excuse  for  the  misplacement  of  the  numinous,  as  it 
might  be  called;  and  the  affirmation  that  biology  must  be  based 
upon  physics  will  cause  less  antagonism  than  in  the  past.  In  a  word, 
the  vitaHsts  wished  to  introduce  mysticism  at  the  wrong  level;  the  right 

32  THE  THEORY  OF  [pt. 

level  would  seem  to  be,  as  it  were,  underneath  the  metrical  abstrac- 
tions of  physics,  i.e.  outside  science  altogether,  and  if  this  is  realised, 
the  vitalist  and  the  mechanist  will  fuse  into  one  and  the  same 
person — a  happy  consummation.  It  is  curious  that  at  the  present 
time,  when  physics  is  so  markedly  freeing  itself  from  scientific 
naturalism,  biologists  are  sometimes  found  to  support  that  untenable 
world-view,  while  still  farther  away  from  the  inorganic  world, 
literary  criticism  tries  to  make  itself  modern  by  using  a  psychological 
jargon,  and  applying  to  its  problems  all  the  rigour  of  a  materialist 

Neo-mechanism  as  a  Theory  for  Chemical  Embryology 

The  principal  philosophical  obstacles  to  physico-chemical  embryo- 
logy have  now  been  assessed  and  nothing  remains  but  to  outline  its 
own  theoretical  basis.  Anyone  who  was  dissatisfied  twenty  years  ago 
with  the  various  forms  of  neo-vitalism  which  have  already  been 
discussed  would  have  had  no  alternative  but  to  accept  the  simple, 
though  rather  incredible,  scientific  naturalism  of  the  preceding 
century,  unless,  indeed,  he  was  acquainted  with  German  philosophy, 
and  understood  the  momentous  consequences  which  flowed  from  the 
apparently  technical  question,  "How  are  a  priori  synthetic  judgments 
possible?"  The  varieties  of  neo-vitalism  may  perhaps  be  thought  of, 
in  so  far  as  they  are  not  modern  forms  of  difficulties  which  have 
for  many  centuries  perplexed  philosophers,  as  a  series  of  reactions 
against  mechanistic  biology  insufficiently  distinguished  from  scientific 
naturalism.  This  confusion  is  well  seen  in  the  earlier  phases  of  the 
American  discussion  which  led  up  to  the  symposium  of  191 8.  It  is 
often  difficult  to  tell,  as  in  the  papers  of  Nichols;  Ritter;  More  and 
Fraser  Harris,  whether  the  writer  is  attacking  the  mechanical  theory 
of  the  universe  regarded  as  an  ultimate  metaphysical  faith  or  the 
mechanical  methodology  of  science. 

Before  the  eighteenth  century,  of  course,  there  had  always  been 
thinkers  who  felt  the  necessity  of  including  both  teleology  and  its 
antithesis  in  their  systems  of  thought.  This  pull  in  two  directions 
accounts  for  those  very  interesting  mediaeval  theologians,  such  as 
Siger  of  Brabant  and  John  of  Jandun,  who  wished  to  acknowledge 
two  kinds  of  truth,  theological  and  philosophical  (see  Maywald  and 
Gilson).  A  right  balance  had  to  be  struck  in  some  way  between 
Democritus  and  Plotinus,  and  in  the  seventeenth  century,  for  in- 


stance,  Sir  Thomas  Browne  wrote  to  his  son  advising  him  to  study- 
Lucretius  yet  not  to  read  too  much  in  him,  "there  being  divers 
impieties  in  him".  Perhaps  the  greatest  figure  in  this  line  of  descent 
is  the  Cardinal  Nicholas  of  Cusa,  who,  in  his  book  De  Docta  Ignorantia 
of  1440,  contended  that  the  principle  of  contradiction  was  only  valid 
for  our  reason,  and  so  foreshadowed  Kant  and  Hegel  (cf.  Vansteen- 
berghe) .  But  the  starry  heavens  with  their  infinite  spaces  that  terrified 
Pascal  and  their  mechanical  order  and  metrical  uniformity  revealed 
by  Kepler  and  Copernicus,  on  the  one  hand,  and  the  moral  law 
with  its  tremendous  purposiveness  and  its  theological  implications, 
on  the  other  hand,  were  never  really  faced  at  one  and  the  same 
moment  and  taken  seriously  together  until  the  time  of  Kant,  who 
first  subjectivated  what  had  before  struggled  in  the  external  world, 
and  suggested  that  the  contradictions  of  our  thought  might  spring 
from  the  constitution  of  our  own  intelligence.  "It  has  always  been 
assumed",  he  said,  "that  all  our  knowledge  must  conform  to  objects. 
The  time  has  now  come  to  ask,  whether  better  progress  may  not  be 
made  by  supposing  that  objects  must  conform  to  our  knowledge." 

Omnis  enim  longe  nostris  ab  sensibus  infra 
primorum  natura  jacet.  .  . 

Lucretius  had  said,  but  Kant  went  farther,  and  suggested  that  our 
intelHgence  can  help  us  no  more  than  our  senses  in  the  attempt 
to  see  things  as  they  really  are. 

This  was  the  great  service  that  Kant  performed  for  philosophy,  and 
in  the  light  of  it  the  scientific  mind  was  relieved  of  the  burden  of 
having  to  believe  finally  in  its  own  account  of  the  world.  But  in  the 
scientific  controversies  of  the  last  century,  Kant  was  forgotten,  and 
the  continual  successes  of  the  scientific  method  led  to  a  naturaUstic 
outlook,  which  was  wholly  unsatisfactory.  It  had  been  supported  by 
T.  H.  Huxley,  Herbert  Spencer,  W.  K.  CUfford,  Tyndall,  Ray 
Lankester,  and  many  others:  it  apparently  still  is  by  Chalmers 
Mitchell.  But,  as  a  widely  accepted  attitude,  it  did  not  live  long  into 
the  present  century,  and  from  such  blows  as  James  Ward's  Naturalism 
and  Agnosticism  and  Antonio  Aliotta's  The  Idealistic  Reaction  against 
Science,  it  never  recovered.  Physico-chemical  biologists  were  thus  left, 
as  it  were,  without  visible  means  of  support,  and  existed  for  some  time 
on  a  purely  pragmatic  basis,  devoid  of  any  epistemological  comfort. 
Gradually,  however,  a  more  satisfactory  attitude  came  into  being. 

34  THE  THEORY  OF  [pt. 

Karl   Pearson   pro\-ided   an  intimation   of  it  when   he  remarked, 
"Those  who  say  that  mechanism  cannot  explain  life  are  perfectly 
correct,  but  then  mechanism  does  not  explain  anything.  Those,  on 
the  other  hand,  who  say  that  mechanism  cannot  describe  hfe  are 
going  far  beyond  what  is  justifiable  in  the  present  state  of  our  know- 
ledge". A  clear  enunciation  of  it,  informed  with  the  charm  of  all 
his  writings,  was  given  by  d'Arcy  Thompson  in  the  .\ristoteUan 
Society^  S\Tnposium  of  191 8.  "In  the  concepts  of  matter  and  energy", 
he  said,  "  the  Whole  is  not  enshrined,  mechanism  is  but  one  aspect 
of  the  world.  These  are  the  proper  categories  of  objective  science, 
but  they  are  no  more:  the  physicist  is,  ipso  facto,  a  mechanist,  but  he 
is  not  by  impHcation  a  materialist;  nor  is  the  biologist  of  necessity 
a  materiahst,  even  though  he  may  study  nothing  but  mechanism  in 
the  material  fabric  and  bodily  acti\ities  of  the  organism."    R.  S. 
Lillie's  paper  of  1927  might  be  taken  as  one  of  the  best  expositions 
of  this  point  of  \-iew.  "Every  biologist  is  aware",  he  says,  "in  his 
non-professional  moments  that  the  possibiUties  of  hfe  are  larger  than 
the  mechanistic  \iew  impHes.  This  is  only  another  way  of  acknow- 
ledging that  the  whole  mechanistic  conception  is  an  incomplete, 
derivative,  or  abstract  one.  To  regard  it  as  philosophically  final  is  a 
grave  mistake."  Thus  Lillie  remains  cominced  of  the  adequacy  of 
physico-chemical  biologv',  but  expressly  repudiates  the  elevation  of 
mechanism  into  a  metaphysic. 

LilUe  goes  on  to  discuss  the  abstract,  distorted  and  incomplete 
character  of  the  world  which  is  presented  to  us  by  the  employment 
of  the  scientific  method.  "To  say",  he  proceeds,  "that  Hfe  is  'nothing 
but'  a  combination  of  chemical  reactions  in  a  colloidal  substratum 
is  unscientific.  Life  may  be  and  apparently  is  that  in  part  but  to 
regard  any  such  scientific  formulation  as  a  complete  and  adequate 
representation  of  its  total  reaUt}-  is  simply  to  misconcei\-e  the  structure 
of  science."  This  is  well  said;  Ufe  is  indeed  a  "dynamic  equihbrium 
in  a  polyphasic  system",  but  also  "Life  is  a  manifest  of  emergent 
creativity",  "Life  is  a  pure  flame  and  we  five  by  an  imisible  sun 
within  us",  "Life  is  a  sad  composition,  we  five  with  death  and  die 
not  in  a  moment",  and — if  you  will, 

Life,  like  a  dome  of  many-coloured  glass, 
Stains  the  white  radiance  of  eternity 
Until  death  tramples  it  to  fi-agments. 


"The  dilemma  of  vitalism  is  irresolvable",  says  Lillie,  "so  long  as 
we  regard  the  units,  concepts,  and  formulae  found  vaHd  in  physical 
science  not  as  abstractions  but  as  primary  and  self-existent  reaUties, 
by  a  combination  of  which  all  the  properties  of  living  beings  as  of 
other  natural  phenomena  can  be  derived." 

In  a  former  discussion  I  contrasted  what  might  be  called  the 
Democritus-Holbach-Huxley  attitude  in  biology  with  the  Driesch- 
Haldane-Russell-Rignano  attitude,  and  concluded  after  examining 
them  that  both  involved  insuperable  difficulties.  Lotze  was  the 
philosopher  to  whom  I  went  for  help  in  the  elaboration  of  a  better 
standpoint.  "The  true  source  of  the  life  of  science",  said  he,  "is  to 
be  found,  not  indeed  in  admitting  now  a  fragment  of  one  view  and 
now  a  fragment  of  the  other,  but  in  showing  how  absolutely  universal 
is  the  extent  and  at  the  same  time  how  completely  subordinate  is 
the  significance  of  the  mission  which  mechanism  has  to  fulfil  in  the 
structure  of  the  world."  And  in  another  place,  "We  granted  v^aUdity 
to  the  mechanical  view  in  so  far  as  concerns  the  examination  of  the 
relations  between  finite  and  finite  and  the  origin  and  accomplish- 
ment of  any  reciprocal  action  whatever;  we  as  decidedly  denied  its 
authority  when  it  claimed  acceptance,  not  as  a  formal  instrument  of 
investigation,  but  as  a  final  theorv'  of  things".  "Nowhere  is  me- 
chanism", says  Lotze,  "the  essence  of  the  matter,  but  nowhere  does 
being  assume  another  form  of  finite  existence  except  through  it." 

I  went  on  to  argue  that,  although  Lotze  made  everv^  effort  to  demon- 
strate how  mechanism  and  teleolog)'  could  fit  together  in  the  universe, 
he  failed  to  do  so  convincingly,  and  that  it  was  more  satisfactory  to 
make  them  necessary  results  of  the  a  priority  of  our  ways  of  thought. 
"We  may  regard",  I  said,  "the  mechanistic  view  of  the  world  as  a 
legitimate  methodological  distortion,  capable  of  appHcation  to  any 
phenomenon  whatever,  and  possessing  no  value  at  all  as  a  meta- 
physical doctrine."  Mechanism,  whichever  of  its  forms  ^defined  by 
C.  D.  Broad,  M.  R.  Cohen  and  Y.  H.  Krikorian  turns  out  to  be 
the  minimum  requirement  of  science,  is,  in  fact,  not  metaphysical 
materiahsm.  It  is  necessary  to  maintain  it  on  methodological  grounds, 
but  it  is  pernicious  to  allot  it  any  v\ider  value.  It  stands,  in  fact, 
as  one  of  the  kinds  of  way  in  which  the  human  spirit  reacts  to  the 
universe  in  which  it  finds  itself,  and  it  springs,  as  R.  G.  CoUingwood 
puts  it,  directly  from  the  ultimate  root  of  all  science,  the  assertion 
of  the  abstract  concept.   "He  who  generaUses  is  an  idiot",  said 


36  THE  THEORY  OF  [pt. 

William  Blake,  but  that  was  a  revelation  of  the  poetic  or  the  religious 
mind.  The  scientific  spirit  is  as  profound  as  these,  but  it  sets  out 
upon  a  different  path  from  the  very  beginning  and  reaches  in  the 
end  a  country  different  in  every  way.  It  directs  its  interest  from  the 
first  to  the  correlation  of  differences  between  phenomena  rather  than 
to  individual  phenomena  themselves,  and  the  impulse  to  classify 
leads  inevitably  to  the  supremacy  of  the  mechanical  cause  and  the 
mathematical  formula.  It  stands  "at  diameter  and  sword's  point" 
with  such  aphorisms  as  "Everything  is  itself  and  not  something  else" 
or  "Nothing  is  ever  merely  anything". 

R.  G.  Collingwood  has  expressed  this  in  a  memorable  passage: 
"Mathematics,  mechanics,  and  materialism  are  the  three  marks  of 
all  science,  a  triad  of  which  none  can  be  separated  from  the  others, 
since  in  fact  they  all  follow  from  the  original  act  by  which  the  scientific 
consciousness  comes  into  being,  namely,  the  assertion  of  the  abstract 
concept.  They  are  all,  it  may  be  said,  products  of  the  classificatory 
frame  of  mind,  corollaries  from  the  fact  that  in  this  frame  of  mind 
the  universal  and  the  particular  are  arbitrarily  separated  and  the 
universal  asserted  in  its  barren  an'd  rigid  self-identity.  It  is  this 
barrenness  and  this  rigidity  which  confer  their  character  upon  the 
doctrines  of  scientific  materialism.  Hence  it  is  idle  to  imagine  that 
materialism  is  justified  in  some  sciences  and  not  in  others.  It  is  idle 
to  protest  that  science  ought  to  surrender  its  materialistic  prejudices 
when  it  finds  itself  face  to  face  with  a  non-material  object  such  as 
the  soul.  No  object  is  material,  in  the  metaphysical  sense  of  the  word, 
except  in  so  far  as  scientific  thinking  conceives  it  so;  for  materiality 
means  abstractness,  subjection  to  the  formulae  of  mechanical  deter- 
mination and  mathematical  calculation,  and  these  formulae  are 
never  imposed  upon  any  object  whatever  except  by  an  arbitrary 
act  which  falsifies  the  object's  nature.  This  only  appears  paradoxical 
when  we  fail  to  see  the  gulf  which  separates  the  common-sense 
materiaHty  of  a  table,  its  sensible  qualities,  from  its  metaphysical 
materiality,  the  abstract  conceptual  substrate  of  those  qualities.  It  is 
this  substrate  whose  transcendent  or  abstract  existence  is  asserted  by 
materialism.  Hence  we  cannot  distinguish  objects  like  tables  which 
are  really  'material'  from  objects  in  whose  presence  science  must 
unlearn  its  materialistic  habits  of  thought.  MateriaHsm  is  no  more 
the  truth  in  physics  than  in  psychology,  and  no  less.  It  is  the  truth 
about  any  object,  just  in  so  far  as  this  object  is  by  abstraction  re- 


ducible  to  terms  of  pure  mathematics;  and  no  object  is  so  reducible 
except  by  consciously  or  unconsciously  shutting  our  eyes  to  every- 
thing which  differentiates  it  from  anything  else.  This  conscious  or 
unconscious  act  of  abstraction  is  the  very  being  of  the  scientific  con- 
sciousness; and  it  is  therefore  no  matter  for  pained  surprise  when 
science  shows  a  bias  towards  determinism,  behaviourism,  and 
materiaHsm  generally". 

By  this  time  the  general  outlines  of  this  theoretical  excursus  should 
have  become  clear.  Embryology,  to  put  it  plainly,  has  been  for  so 
many  years  the  happy  hunting-ground  of  vitaHstic  and  neo-vitalistic 
theory  that  the  first  treatise  on  the  physico-chemical  aspect  of  it 
could  hardly  go  without  some  kind  of  theoretical  introduction. 
"VitaHstic  conceptions",  said  Claude  Bernard  in  1875,  with  the 
voice  of  authentic  prophecy,  "can  no  longer  hover  over  physiology 
as  a  whole.  The  developmental  force  of  the  egg  and  the  embryonic 
cells  is  the  last  rampart  of  vitalism,  but  in  taking  refuge  there,  it 
transforms  itself  into  a  metaphysical  concept  and  snaps  the  last  link 
connecting  it  with  the  physical  world,  and  the  science  of  physiology." 

It  is  to  be  hoped  that  what  has  now  been  said  will  place  in  a  right 
light  the  aims  of  physico-chemical  embryology,  and  provide  it,  as 
it  were,  with  its  decretals.  That  they  are  not  false  will  be  the  hope 
of  every  exact  biologist. 

Chemical  embryology  is  now  indeed  at  a  critical  point  in  its 
history.  On  the  one  hand,  it  links  up  with  the  morphological  work 
of  the  classical  embryology  and  the  experimental  work  of  the 
Entwicklungsmechanik  school,  while  on  the  other  hand  it  has 
affinities  with  genetics,  a  science  which  is  every  day  becoming  more 
physiological  and  which  will  more  and  more  seek  for  the  effects 
of  its  factors  in  the  biochemistry  of  development.  Goldschmidt's 
book,  and  the  work  of  Dunn,  who  found  a  lethal  gene  in  an  inbred 
strain  of  fowl  which  caused  a  regular  chick  mortaUty  at  the  seven- 
teenth day  of  incubation,  are  important  examples  of  this.  Another 
relationship  of  chemical  embryology  is  to  obstetric  medicine,  for  such 
problems  as  the  toxaemias  of  pregnancy  will  not  be  solved  by  Hippo- 
cratic  observation  unassisted  by  a  knowledge  of  the  chemistry  of 
the  embryo  and  the  placenta.  The  attention  devoted  by  the  Medical 
Research  Council  to  such  problems  is  an  acknowledgment  of  this 
fact.  Nor  is  veterinary  physiology  in  a  position  to  do  without  the 
aid  of  chemico-embryological  researches,  as  is  shown  by  the  incident 


of  the  myxoedematous  pig  foetuses  of  western  America  in  the  work 
of  Smith. 

But  all  practical  applications,  how  valuable  soever,  must  give 
place  to  the  increase  of  knowledge  itself,  and  therefore  the  physico- 
chemical  history  of  embryonic  development,  from  the  egg-cell  to  the 
loosing  of  the  individual  into  the  activity  of  post-natal  life,  is  to  be 
the  theme  of  this  present  book.  "The  history  of  a  man  for  the  nine 
months  preceding  his  birth",  said  S.  T.  Coleridge,  "would  probably 
be  far  more  interesting,  and  contain  events  of  far  greater  moment 
than  all  the  three-score  and  ten  years  that  follow  it." 






Nobilissimo  juveni  Medico  Philippo 

de    Glarges,   amicitiae   ergo   libenter 

Gulielmus  Harveus  scripsit,  Anglus, 

Med.  Reg.  et  Anat.  Prof.   Londin. 

Mai.  8  1641 

From  the  commonplace  book  of 
Philip  de  Glarges. 

Not  to  prayse  or  disprayse :  all  did  well. 

William  Harvey's  MS.  notes, 
Canones  Anatomiae  Generalis,  6. 


It  is  open  to  anyone  to  say  with  some  appearance  of  truth  that 
physico-chemical  embryology  has  no  history,  since  the  attempt  to 
unravel  the  causes  of  embryological  phenomena  by  physico-chemical 
means  has  only  recently  begun.  But  such  a  statement  would  betray 
a  superficial  and  jejune  mentality.  Physico-chemical  embryology  has 
its  roots  in  the  history  of  embryology  as  a  whole,  and  it  is  those  roots 
which  I  shall  try  to  uncover  in  what  follows.  It  must  be  remembered 
that  morphological  must  theoretically  precede  biophysical  analysis, 
as  it  has  actually  preceded  it  chronologically,  and  to  that  extent 
physico-chemical  embryology  cannot  be  properly  understood  without 
reference  to  its  descriptive  husks,  and  their  historical  growth.  More- 
over, even  in  antiquity  there  are  hints  that  the  chemistry  of  the 
embryo  was  dimly  envisaged  (as  in  Aristotle,  see  p.  70).  Again,  that 
philosophical  problem  which  we  have  already  considered,  plays  a  great 
part  in  the  history  of  embryology,  and  as  we  watch  the  pendulum  swing- 
ing from  Democritus  to  Aristotle,  back  again  over  to  Herophilus, 
and  back  once  more  to  Galen,  we  almost  feel  as  if  we  were  spectators 
looking  on,  like  Hardy's  spirits,  at  a  great  drama,  with  the  movement  of 
which  we  are  powerless  to  interfere,  but  knowing  that  the  existence  of 
exact  biology  depends  upon  which  side  wins.  Lastly,  such  unmorpho- 
logical  questions  as  the  respiration  and  nutrition  of  the  embryo  were 
discussed  from  the  most  ancient  times,  and  it  is  surely  no  unduly  wide 
interpretation  of  the  word  which  leads  us  to  include  an  account  of 
these  opinions  under  the  heading  of  chemico-embryological  history. 
Nor  could  the  present  moment  be  more  appropriate  for  such  an 
historical  survey.  Embryology  is  entering  a  new  phase:  and  on  the 
threshold  it  is  very  fitting  that  some  retrospective  attention  should 
be  paid  to  the  phases  which  it  has  already  passed  through.  The 
events  of  the  past,  moreover,  throw  Hght  on  those  of  the  future,  and 
this  is  true  not  necessarily  in  Spengler's  sense  but  also  because  the 
historical  approach  to  problems  actually  unsolved  protects  them, 
by  a  kind  of  gentle  scepticism,  from  too  severe  a  subjection  to  doc- 
trinaire presentations.  "Die  Geschichte  einer  Wissenschaft  ist  der 
Hort  ihrer  Freiheit;  sie  duldet  ihr  keine  einseitige  Beherrschung", 
said  Louis  Choulant  in  1842.  Theoretical  bhnd  alleys,  such  as  the 
final  cause,  practical  blind  alleys,  such  as  preformationism  and 
phlogiston,  are  always  able  to  remind  us  that  we  may  be  mistaken. 


No  exhaustive  treatise  on  the  history  of  embryology  at  present 
exists.  The  nearest  approach  to  it  is  the  very  valuable  memoir  of 
Bruno  Bloch  with  its  epitome  but  this  only  covers  the  era  of  the 
Renaissance  with  thoroughness.  Hertwig's  account,  which  he  printed 
at  the  beginning  of  his  great  Handbuch  der  Entwicklungslehre,  does  not 
deal  very  fully  with  any  aspect  of  the  subject  before  1800,  nor  do 
the  much  shorter  ones  of  Henneguy  and  Minot.  The  latter  paper  is 
interesting  in  that  it  ends  with  an  emphasis  on  the  need  for  a  physico- 
chemical  attitude  in  the  future.  The  introduction  to  Keibel's  book 
is  much  slighter,  but  contains  some  useful  information.  There  are 
various  monographs  and  papers  on  special  points,  such  as  Pouchet's 
rather  untrustworthy  treatment  of  the  embryology  of  Aristotle,  and 
Lones'  discussion  of  it,  which  is  worse.  Camus'  notes  are  still  the  best 
commentary  on  the  Historia  Animalium.  Again,  useful  information  on 
some  cultural  points  is  to  be  had  from  the  treatise  of  Ploss  &  Bartels. 
The  introductions  to  certain  books  also  contain  valuable  information, 
and  in  this  class  comes  Dareste's  remarkable  book  on  teratology. 
The  bibliographies  contained  in  v.  Haller's  eighth  volume  and  in 
Heffter's  book,  are,  naturally,  of  the  greatest  assistance. 

These  reservations  made,  the  principal  reviews  of  the  subject  are 
chiefly  to  be  found  in  histories  of  science  in  general,  such  as  Sarton's; 
histories  of  biological  theory,  such  as  Radl's;  histories  of  obstetrics, 
such  as  V.  Siebold's,  Spencer's  and  Fasbender's;  histories  of  gynaeco- 
logy, such  as  McKay's;  and  histories  of  anatomy,  such  as  Singer's 
and  V.  Toply's.  Histories  of  medicine  as  a  whole  are  numerous 
and  helpful:  I  have  found  those  of  Garrison  and  Neuburger- 
Pagel  most  useful.  Those  which  deal  with  special  periods  are  also 
of  assistance,  such  as  Schrutz  and  Browne  on  Arabian,  Bloch  on 
Byzantine,  and  Harnack  on  Patristic  medicine.  Histories  of  chemistry 
provide  no  help,  for  ancient  chemistry  was  so  oriented  towards 
"practical"  results,  such  as  the  lapis  philosophorum  and  elixir  vitae, 
that  the  egg  was  only  considered  as  a  raw  material  for  various 
preparations.  The  investigation  of  its  change  of  properties  during 
the  development  of  the  embryo  did  not  occur  to  the  alchemists. 
Detailed  studies  of  particular  subjects,  such  as  those  contained  in 
Singer's  two  excellent  volumes  The  History  and  Method  of  Science, 
may  also  be  of  some  assistance.  Again,  there  are  books  which  give 
a  wonderful  orientation  and  an  articulate  survey  of  vast  tracts :  of 
these  Clifford  Allbutt's  Greek  Medicine  in  Rome,  with  its  mass  of 
references,  is  among  the  most  valuable.  And  Miall's  Early  Naturalists 


must  not  be  omitted,  for,  apart  from  the  peculiar  charm  of  style  which 
marks  it,  it  contains  some  singularly  helpful  bibliographical  data.  But 
the  study  of  the  original  sources,  so  far  as  that  is  possible,  is  a  duty 
which  cannot  be  avoided,  and  in  what  follows  I  have  been  careful 
to  copy  down  no  statement  from  a  previous  review  when  it  was 
possible  to  read  the  actual  words  of  the  writer  himself. 

This  practice  of  going  to  the  originals  is  made  peculiarly  necessary 
in  a  case  such  as  the  present  one,  when  the  history  of  a  subject  is 
to  be  regarded  from  an  entirely  new  angle.  My  intention  is  to  give 
here  the  sketch  of  a  history  of  embryology  consistently  from  the 
physico-chemical  angle,  and  to  show,  at  one  and  the  same  time,  how 
our  knowledge  of  the  development  of  the  embryo  has  come  into  being, 
and  how  throughout  the  process  what  we  now  call  the  physico- 
chemical  foundations  of  embryonic  growth  have  from  time  to  time 
received  attention,  even  though  it  was  largely  speculative.  Since  few 
have  previously  examined  the  history  of  the  subject,  and  none  from 
this  angle,  I  have  in  many  cases  come  upon  interesting  facts  which 
have  remained  unknown  owing  to  the  very  attitude  of  mind  pre- 
viously adopted. 

Finally,  I  would  defend  the  arrangement  of  my  Sections  only  on 
the  ground  that  it  is  suitable  in  the  present  state  of  historical  know- 
ledge. I  say  little  about  embryology  in  ancient  China  and  ancient 
India,  because  on  the  basis  of  what  we  know  there  is  little  to  say, 
not  because  it  was  intrinsically  less  interesting  than  the  embryology 
of  Mediterranean  antiquity  and  the  later  West,  though  this  may  turn 
out  to  be  the  case.  I  do  not  propose  a  framework  for  historical  facts 
in  what  follows ;  I  only  attempt  to  bring  them  together,  and  to  reveal 
some  of  the  relationships  between  them.  If  the  traditional  frame- 
work turns  out  to  be  badly  constructed — and  there  are  many  signs 
that  it  may — the  facts  can  be  rearranged. 

The  history  of  single  forms  of  scientific  knowledge  is  in  a  way 
happier  because  containing  more  of  continuity  than  that  of  civilisa- 
tion as  a  whole.  The  assiduity  with  which  men  of  different  periods 
in  the  rise  and  decHne  of  a  culture  pursue  the  different  forms  of 
human  experience  may,  as  Spengler  has  shown,  vary  much,  but  those 
forms  remain  fundamentally  the  same,  even  if  their  manifestations 
are  profoundly  changed.  That  science,  at  any  rate,  does  maintain 
some  sort  of  continuity  whatever  gaps  there  may  be  between  the 
phases  of  its  progress,  is  a  belief  agreeable  with  all  the  available  facts, 
and  one  which  no  criticism  will  easily  shake. 



I -I.    Non-Hellenic  Antiquity 

Since  biological  science  as  a  whole  was  little  cultivated  in  ancient 
Egypt  and  the  ancient  civilisations  of  Babylonia,  Assyria  and  India, 
the  study  of  embryology,  we  may  assume,  was  equally  little  pursued. 
Doubtless  the  undeveloped  embryo, 
whether  in  egg  or  uterus,  carried 
with  it,  for  these  persons  of  remote 
antiquity,  some  flavour  of  the  ob- 
scene in  the  literal  sense  of  the  word. 
But  embryology  stands  in  a  peculiar 
relation  to  the  history  of  humanity, 
in  that  even  at  the  most  remote  times 
children  were  being  born,  and, 
though  the  practitioners  of  ancient 
folk-medicine  might  confine  their 
ideas  for  the  most  part  to  simple 
obstetrics,  they  yet  could  hardly 
avoid  some  slight  speculation  on  the 
growth  and  formation  of  the  embryo. 
Fig.  I  illustrates  this  level  of  culture. 
It  is  a  painted  and  carved  door  from 
a  house  in  Dutch  New  Guinea,  taken 
from  de  Clercq's  book;  the  original 
was  of  yellowish  brown  wood.  The 
male  embryo  is  clearly  shown,  but 
the  artist  evidently  had  a  hazy  con- 
ception of  the  umbilical  cord.  The 
line  passing  from  the  uterus  to  the  head  may  or  may  not  be  merely 
ornamental.  The  movement  of  the  foetus  in  utero  played  and  still 
plays  a  large  part  in  the  folklore  of  primitive  peoples,  as  may  be  read  in 
the  exhaustive  treatise  of  Ploss  &  Bartels.  For  information  concerning 
god-embryos  in  primitive  religion  see  Briffault. 

Ancient    Indian    embryology   achieved    a   relatively   high    level. 
Structures  such  as  the  amniotic  membrane  are  referred  to  in  the 


I .    Painted  and  carved  door  from 
New  Guinea  (de  Clercq). 


Bhagavad-Gitd.  Susriita  believed  that  the  embryo  was  formed  of  a 
mixture  of  semen  and  blood,  both  of  which  originated  from  chyle. 
In  the  third  month  commences  the  differentiation  into  the  various 
parts  of  the  body,  legs,  arms  and  head,  in  the  fourth  follows  the 
distinct  development  of  the  thorax,  abdomen  and  heart,  in  the  sixth 
are  developed  hair,  nails,  bones,  sinews  and  veins,  and  in  the  seventh 
month  the  embryo  is  furnished  with  any  other  things  that  may  be 
necessary  for  it.  In  the  eighth  there  is  a  drawing  of  the  vital  force 
to  and  from  mother  and  embryo  (is  this  comparable  with  the 
Hippocratic  eXKeiv?  see  Peck)  which  explains  why  the  foetus  is  not 
yet  viable.  The  hard  parts  of  the  body  are  derived  from  the  father, 
the  soft  from  the  mother.  Nourishment  is  carried  on  through  vessels 
which  lead  chyle  from  mother  to  foetus.  (For  further  details  see 
Vullers.)  Ancient  Chinese  embryology  was  very  similar,  if  we 
may  judge  from  Hureau  de  Villeneuve;  Maxwell  &  Liu  and  von 

Egyptian  medicine  did  not  venture  on  embryological  speculation, 
or  so  it  would  seem  from  the  writings  which  have  come  down  to 
us — the  Ebers  medical  papyrus  does  not  once  mention  the  embryo 
(Brugsch) .  But  there  are  points  of  interest  as  regards  Egypt  in  this 
connection.  The  Egyptians  were  responsible  for  one  of  the  greatest 
helps  in  systematic  embryological  study,  namely,  the  discovery  of  the 
artificial  incubation  of  the  eggs  of  birds.  The  success  of  this  process  was 
to  have  so  obvious  an  effect  on  embryology  and  the  abortive  attempts 
to  bring  it  to  completion  were  so  frequent  in  the  West  right  up  to 
the  nineteenth  century  a.d.  that  it  is  remarkable  to  find  artificial 
incubation  practised  "probably",  in  Cadman's  words,  "as  far  back 
as  the  dawn  of  the  Old  Kingdom,  about  3000  B.C."  It  is  doubtful 
whether  the  very  remote  date  could  be  supported  by  Egyptological 
evidence,  for,  according  to  Hall  and  Lowe,  hens  were  not  introduced 
into  Egypt  from  Mesopotamia  or  India  until  the  time  of  the  eighteenth 
dynasty  {ca.  1400  b.g.)  when  there  was  much  intercourse  with  the 
East  (cf  Queen  Tiy  and  the  Tell-el-Amarna  correspondence) :  before 
then  the  Egyptians  had  only  goose  or  duck's  eggs.  Artificial  incubation 
is  certainly  as  old  as  Diodorus  Siculus  and  Pliny,  for  both  of  them 
refer  to  the  practice,  the  latter  in  connection  with  a  curious  piece  of 
ancient  sympathetic  magic.  "  Livia  Augusta,  theEmpresse,"  says  Pliny, 
"wife  sometime  of  Nero,  when  she  was  conceived  by  him  and  went 
with  that  child  (who  afterwards  proved  to  be  Tiberius  Caesar)  being 

46  EMBRYOLOGY   IN   ANTIQ^UITY  [pt.  ii 

very  desirous  (like  a  yong  fine  lady  as  she  was)  to  have  a  jolly  boy, 
practised  this  girlish  experiment  to  foreknow  what  she  should  have 
in  the  end;  she  tooke  an  egge,  and  ever  carried  it  about  her  in  her 
warme  bosome;  and  if  at  any  time  she  had  occasion  to  lay  it  away, 
she  would  convey  it  closely  out  of  her  own  warme  lap  into  her 
nurses  for  feare  it  should  chill.  And  verily  this  presage  proved  true, 
the  egge  became  a  cocke  chicken,  and  she  was  delivered  of  a  sonne. 
And  hereof  it  may  well  be  came  the  device  of  late,  to  lay  egges  in 
some  warme  place  and  to  make  a  soft  fire  underneath  of  small  straw 
or  light  chaffe  to  give  a  kinde  of  moderate  heate ;  but  evermore  the 
egges  must  be  turned  with  a  mans  or  womans  hand,  both  night  and 
day,  and  so  at  the  set  time  they  looked  for  chickens  and  had  them" 
(Philemon  Holland's  translation). 

Pliny  also  says,  "Over  and  besides  there  be  some  egs  that  will 
come  to  be  birds  without  sitting  of  the  henne,  even  by  the  worke 
of  Nature  onely,  as  a  man  may  see  the  experience  in  the  dunghills 
of  Egypt.  There  goeth  a  prettyjeast  of  a  notable  drunkard  of  Syracusa, 
whose  manner  was  when  hee  went  into  the  Taverne  to  drinke  to  lay 
certaine  egges  in  the  earth,  and  cover  them  with  moulde,  and  he 
would  not  rise  nor  give  over  bibbing  untill  they  were  hatched.  To 
conclude,  a  man  or  a  woman  may  hatch  egges  with  the  very  heate 
onely  of  their  body".  This  story  occurs  also  in  Aristotle. 

The  Emperor  Hadrian — curiositatum  omnium  explorator  as  Tertullian 
calls  him — writing  in  a.d.  130  to  his  brother-in-law,  L.  Julius 
Servianus,  from  Egypt,  says,  "I  wish  them  no  worse  than  that 
they  should  feed  on  their  own  chickens,  and  how  foully  they  hatch 
them,  I  am  ashamed  to  tell  you".  In  the  Description  de  VEgypte, 
written  by  the  members  of  the  scientific  staff  of  Napoleon's  Egyptian 
expedition,  and  published  at  Paris  in  1809,  Roziere  and  Rouyer 
wrote  on  the  artificial  incubation  of  the  Egyptians.  They  conjecture 
very  probably  that  the  Emperor  was  shocked  owing  to  a  misunder- 
standing shared  by  Aristotle,  PUny,  de  Pauw  and  Reaumur,  namely, 
that  the  "gelleh"  or  dung  was  used  to  heat  the  eggs  by  its  fermenta- 
tion, and  not,  as  is  and  was  actually  the  case,  by  being  slowly  burnt 
in  the  incubation  ovens.  Bay  gave  an  account  of  the  ovens  in  modern 
times,  but  the  best  one  is  that  of  Lane.  "The  Egyptians",  said  Lane 
in  1836,  "have  long  been  famous  for  hatching  fowls'  eggs  by  artificial 
heat.  This  practice,  though  obscurely  described  by  ancient  authors, 
appears  to  have  become  common  in  ancient  Egypt  from  an  early 

PLATE   1 

(from  Cadman) 

(from  King) 


time.  In  Upper  Egypt  there  are  over  fifty  establishments,  and  in 
Lower  Egypt  more  than  a  hundred.  The  furnace  is  constructed  of 
sun-dried  bricks  and  consists  of  two  parallel  rows  of  small  ovens  and 
cells  for  fire  divided  by  a  narrow  vaulted  passage,  each  oven  being 
about  9  or  10  feet  long,  8  feet  wide  and  5  or  6  feet  high,  and  having 
above  it  a  vaulted  fire-cell  of  the  same  size  but  rather  less  in  height. 
The  eggs  are  placed  upon  mats  or  straw,  one  tier  above  another 
usually  to  the  number  of  three  tiers  and  the  burning  fuel  is  placed 
upon  the  floors  of  the  fire-cells  above.  The  entrance  of  the  furnace  is 
well  closed.  Each  furnace  consists  of  from  twelve  to  24  ovens  and 
receives  about  150,000  eggs  during  the  annual  period  of  its  con- 
tinuing open,  one  quarter  or  one  third  of  which  generally  fail.  The 
peasants  supply  the  eggs  and  the  attendants  examine  them  and  after- 
wards generally  give  one  chicken  for  every  two  eggs  that  they  have 
received.  The  general  heat  maintained  during  the  process  is  from 
100  to  103  of  Fahrenheit's  thermometer.  The  manager,  having  been 
accustomed  to  the  art  from  his  youth,  knows  from  long  experience 
the  exact  temperature  that  is  required  for  the  success  of  the  operation 
without  having  any  instrument  like  our  thermometer  to  guide  him. 
The  eggs  hatch  after  exactly  the  same  period  as  in  the  case  of  natural 
incubation.  I  have  not  found  that  the  fowls  produced  in  this  manner 
are  inferior  in  point  of  flavour  or  in  other  respects  to  those  produced 
from  the  egg  in  the  ordinary  way."  The  accompanying  picture 
(Plate  I  a),  taken  from  Cadman,  shows  the  interior  of  a  modern 
peasant's  incubator.  There  is  reason  to  beheve  that  its  construction 
and  operation  vary  very  little,  if  at  all,  from  that  of  the  ovens  used  in 
dynastic  Egypt. 

When  Bay  visited  the  native  incubators  in  191 2  he  took  with  him 
a  flask  of  lime  water  and  a  thermometer.  The  former  showed  a  large 
precipitation  of  calcium  carbonate  and  the  latter  stood  at  40°  C.  He 
was  led  to  speculate  on  the  value  of  a  high  CO2  tension  in  the  at- 
mosphere, and  concluded  that  it  must  have  a  beneficial  effect,  since 
the  loss  in  the  native  incubator  was  not  more  than  4  per  cent.,  while 
that  in  the  oil-heated  agricultural  incubators  of  his  time  was  as 
much  as  40  per  cent.  Cadman,  writing  in  1921,  suggests  that  the 
well-known  non-sitting  instinct  of  Egyptian  poultry  is  an  effect  of 
the  ancient  practice  of  artificial  incubation.  But  enough  has  been 
said  of  the  Egyptian  "Ma'mal  al  katakeet",  or  chicken  factory. 
In  spite  of  the  remarkable  opportunity  thus  afforded  for  acquiring 


facts  in  experimental  embryology,  no  use  was  apparently  ever  made 
of  it,  though  there  seems  to  be  a  certain  amount  of  traditional 
information  current  among  the  peasant  operators,  as,  for  example, 
that  the  "ruh"  or  life  enters  into  the  egg  at  the  eleventh  day.  It 
w^ould  be  interesting  to  investigate  this  aspect  of  the  subject  further. 

In  ancient  China  also  it  would  appear  that  artificial  incubation 
was  successfully  carried  on  in  remote  antiquity,  if  we  may  judge  by 
the  account  given  by  King.  Native  incubation  in  China  is  carried 
on  in  wicker  baskets,  heated  with  charcoal  pans  (Plate  Ib).  The 
attendants  sleep  in  the  incubator  itself,  and  use  the  same  thermometer 
as  the  Egyptians,  namely,  their  eyelids,  to  which  they  apply  the  blunt 
end  of  the  egg.  The  Egyptian  success  was  known  generally  in  the 
West  in  later  times  though  it  could  not  be  imitated. ' '  The  Aegyptians ' ' , 
said  Sir  Thomas  Browne,  "observed  a  better  way  to  hatch  their 
Eggs  in  Ovens,  than  the  Babylonians  to  roast  them  at  the  bottom  of 
a  sling,  by  swinging  them  round  about,  till  heat  from  motion  had 
concocted  them;  for  that  confuseth  all  parts  without  any  such  effect." 
Browne's  slightly  rueful  tone  suggests  that  he  tried  it  himself.  It  is 
interesting  that  this  quaint  experiment  was  the  cause  of  a  controversy 
between  Sarsi,  who  asserted  on  the  authority  of  Suidas  that  it  was 
possible,  and  GaHleo,  who  thought  the  idea  ridiculous.  Modern  work 
on  the  instability  of  albumen  solutions,  such  as  that  of  Harris,  lends 
some  colour  to  the  legend.    (See  p.  275.) 

Ancient  Egypt  supplies  the  starting-point  for  another  and  pro- 
founder  train  of  thought  which  recurs  constantly  throughout  the 
history  of  embryology,  and  to  which  I  shall  have  to  refer  again  more 
than  once.  This  was  concerned  with  the  problem  of  deciding  at  what 
point  the  immortal  constituent  universally  regarded  as  existing  in 
living  beings  took  up  its  residence  in  the  embryo.  Some  fragments 
of  ancient  Indian  philosophy  assure  us  that  the  Vedic  writers  occupied 
themselves  with  this  question,  and  according  to  Crawley  the  Avesta 
theorises  upon  it.  But  as  early  as  1400  B.C.,  i.e.  during  the  eighteenth 
dynasty  in  Egypt,  something  was  said  regarding  this,  for  we  have 
extant  at  the  present  day  a  very  beautiful  hymn  to  the  sun-god, 
Aton,  written  by  no  less  a  person  than  Akhnaton  (Nefer-kheperu-Ra 
Ua-en-Ra,  Amen-hetep  Neter  heq  Uast),  generally  known  as 
Amenophis  IV  or  the  "heretic"  king,  who  abandoned  the  traditional 
worship  of  the  Theban  god  Amen-Ra  and  established  an  Aton-cult, 
as  has  been  described  by  Baikie  and  others.   One  of  his  hymns,  which 


bears   considerable   resemblance   to   the  one  hundred   and   fourth 
psalm,  runs  as  follows  (in  Breasted's  translation) : 

{the  sun- god  is  addressed) 

Creator  of  the  germ  in  woman, 

Maker  of  seed  in  man, 

Giving  life  to  the  son  in  the  body  of  his  mother, 

Soothing  him  that  he  may  not  weep, 

Nurse  (even)  in  the  womb. 

Giver  of  breath  to  animate  every  one  that  he  maketh 

When  he  cometh  forth  from  the  womb  on  the  day  of  his  birth. 

Thou  openest  his  mouth  in  speech. 
Thou  suppliest  his  necessity. 

When  the  fledgling  in  the  egg  chirps  in  the  shell 
Thou  givest  him  breath  therein  to  preserve  him  alive. 
When  thou  hast  brought  him  together 
To  the  point  of  bursting  out  of  the  egg, 
He  cometh  forth  from  the  egg 
To  chirp  with  all  his  might. 

He  goeth  about  upon  his  two  feet 
When  he  hath  come  forth  therefrom. 

The  important  point  here  is  that  life  =  soul.  At  this  early  period 
there  is  no  trace  of  the  notions  which  appear  later,  such  as  the  idea 
that  embryos  are  not  aUve  until  the  time  of  birth  or  hatching,  or 
the  idea  that  the  soul  is  breathed  into  the  embryo  at  some  particular 
point  in  development.  But  in  later  times  these  considerations  carried 
great  weight,  and  with  the  rise  of  theology  a  definite  stand  had  to 
be  taken  about  them,  for  otherwise  no  ethical  status  could  be  assigned 
to  abortion.  Speculation  on  these  matters  has  continued  without 
cessation  since  the  time  of  Akhnaton,  reaching  a  climax  perhaps  in 
Christian  times  with  Cangiamilla's  Embryologia  Sacra,  and  living  on 
embedded  in  Roman  Catholic  theology  up  to  our  own  era.  In  the 
last  century  the  subject  seems  to  have  had  a  special  fascination  for 
Ernst  Haeckel,  who  frequently  mentioned  it.  But  the  future  holds  no 
place  for  the  discussion  of  such  themes,  and  what  has  been  called 
"theological  embryology"  is  already  dead,  though  we  may  perhaps 
descry  its  successor,  psychological  embryology,  in  such  researches  as 
those  of  Teuscher,  Cesana,  y  Gonzalez,  Swenson  and  Coghill. 


Ancient  Greek  thought  shows  many  evidences  of  appreciation  of 
the  mystery  of  embryonic  growth,  as  for  example 
in  the  Orphic  cosmogonies,  which  had  their  origin 
about  the  seventh  or  eighth  century  b.g.  In  these 
rehgious  and  legendary  descriptions  of  the  world, 
which  have  been  exhaustively  discussed  by  A.  B. 
Cook  and  F.  Lukas,  the  cosmic  egg  plays  a  large 
part,  and  has  been  shown  to  occur  also  in  the     .         ^      ,      , . 

.  •  f  T^  T     1-        -r.       •  1    Fig- 2.   Eros  hatching 

ancient  cosmogonies  ot  Lgypt,  India,  Persia  and  from  the  cosmic  egg. 
Phoenicia.  A  familiar  reference  to  this  cosmic  (A  Hellenistic  gem  de- 
egg,  out  of  which  all  things  were  produced  at  ^^^^  ^  y  .  .  oo  .j 
the  beginning  of  the  world,  is  in  Aristophanes'  comedy.  The  Birds, 
where  the  owl,  as  leader  of  the  Chorus,  says  in  the  Parabasis 
(J.  T.  Sheppard's  translation) : 

Chaos   was   first,   and    Night,   and  the   darkness    of  Emptiness,   gloom 

tartarean,  vast ; 
Earth  was  not,  nor  Heaven,  nor  Air,  but  only  the  bosom  of  Darkness ; 

and  there  with  a  stirring  at  last 
Of  wings,  though  the  wings  were  of  darkness  too,  black  Night  was  inspired 

a  wind-egg  to  lay. 
And  from  that,  with  the  turn  of  the  seasons,  there  sprang  to  the  light 

the  Desired, 
Love,  and  his  wings  were  of  gold,  and  his  spirit  as  swift  as  the  wind  when 

it  blows  every  way. 
Love  moved  in  the  Emptiness  vast,  Love  mingled  with  Chaos,  in  spite  of 

the  darkness  of  Night, 
Engendering  us,  and  he  brought  us  at  last  to  the  light. 

And  perhaps  another  reference  to  the  place  of  the  egg  in  ancient 
cosmogony  occurs  in  The  Arabian  Nights,  where  Aladdin's  request 
for  a  roc's  egg  is  treated  as  a  blasphemy  by  the  genie.  Still  more 
fantastic  is  the  speculation  of  C.  H.  Rice  (in  Psyche,  1929!)  that  the 
world  is  an  egg;  living  matter  being  the  embryo  and  inorganic 
matter  the  yolk.  But  none  of  the  facts  which  have  so  far  been 
mentioned  bears  more  than  obliquely  upon  the  main  centre  of 
interest,  the  study  of  embryology.  For  its  direct  ancestry,  Greece,  as 
might  be  expected,  is  responsible. 

1-2.    Hellenic  Antiquity:  the  Pre-Socratics 

The  pre-Socratic  philosophers  nearly  all  seem  to  have  had  opinions 
upon  embryological  phenomena,  many  of  which  are  worth  referring 


to.  These  investigators  of  nature  who  Hved  in  Greece  from  the  eighth 
century  onwards  are  only  known  to  us  through  the  writings  of 
others,  or  in  some  cases  in  the  form  of  fragments,  for  all  their 
complete  books  have  perished.  Diels'  collection  of  the  Fragmente  der 
Vorsokratiker  is  the  most  convenient  source  for  what  is  left,  but  the 
assembling  of  their  opinions  has  not  been  left  to  modern  times,  for 
a  collection  of  them  occurs  in  the  writings  of  Plutarch  of  Chaeronea^ 
(3rd  century  a.d.).  It  is  necessary  to  make  use  of  some  caution 
in  describing  their  views,  for  Aristotle,  as  an  instance,  frequently 
gives  the  most  unfair  versions  of  the  views  of  his  predecessors.  The 
account  which  follows  is  based  upon  Plutarch,  in  Philemon  Holland's 
translation,  and  Diels.  Empedocles  of  Akragas,  who  lived  about 
444  B.C.,  believed  that  "the  embryo  derives  its  composition  out  of 
vessels  that  are  four  in  number,  two  veins  and  two  arteries,  through 
which  blood  is  brought  to  the  embryo".  He  also  held  that  the  sinews 
are  formed  from  a  mixture  of  equal  parts  of  earth  and  air,  that 
the  nails  are  water  congealed,  and  that  the  bones  are  formed  from 
a  mixture  of  equal  parts  of  water  and  earth.  Sweat  and  tears,  on 
the  other  hand,  are  made  up  of  four  parts  of  fire  to  one  of  water. 
Empedocles  also  had  opinions  about  the  origin  of  monsters  and  twins, 
and  asserted  that  the  influence  of  the  maternal  imagination  upon  the 
embryo  was  great  so  that  its  formation  could  be  guided  and  interfered 
with.  "Empedocles",  says  Plutarch,  "saith  that  men  begin  to  take 
forme  after  the  thirtie-first  day  and  are  finished  and  knit  in  their 
parts  within  50  dales  wanting  one.  Asclepiades  saith  that  the  members 
of  males  because  they  are  more  hot  are  joynted  and  receive  shape  in 
the  space  of  26  dales,  and  many  of  them  sooner,  but  are  finished  and 
complet  in  all  limbes  within  50  dales  but  females  require  two  moneths 
ere  they  be  fashioned,  and  fower  before  they  come  to  their  perfection, 
for  that  they  want  naturall  heat.  As  for  the  parts  of  unreasonable 
creatures  they  come  to  their  accomplishment  sooner  or  later,  ac- 
cording to  the  temperature  of  their  elements."  Empedocles  did  not 
consider  that  an  embryo  was  fully  alive.  "Empedocles ",  says  Plutarch, 
"denieth  it  to  be  a  creature  animall,  howbeit  that  it  hath  life  and 
breath  within  the  bellie,  mary  the  first  time  that  it  hath  respiration 
is  at  the  birth,  namely,  when  the  superfluous  humiditie  which  is  in 
such  unborne  fruits  is  retired  and  gone,  so  that  the  aire  from  without 
entreth  into  the  void  vessels  lying  open." 

^  It  is  now  certain  that  this  collection  is  not  by  Plutarch  himself  but  by  an  earlier 
compiler,  Aetius  (see  Burnet). 



Anaxagoras  of  Clazomenae  (500-428  B.C.)  may  have  said  that  the 
milk  of  mammals  corresponded  to  the  white  of  the  fowl's  egg,  but 
that  observation  is  also  attributed  to  Alcmaeon  of  Croton.  It  is  more 
certain  that  he  spoke  of  a  fire  inside  the  embryo  which  set  the  parts 
in  order  as  it  developed,  and  that  the  head  was  the  part  to  be  formed 
first  in  development.  This  thesis  was  supported  by  Alcmaeon,  and 
by  Hippon  of  Samos,  a  Pythagorean,  in  the  fifth  century  B.C.,  but 
Diogenes  of  Apollonia  maintained  about  the  same  time  that  a  mass 
of  flesh  was  formed  first,  and  afterwards  the  bones  and  nerves  were 
differentiated.  Plutarch  remarks  about  this:  "Alcmaeon  affirmeth 
that  the  head  is  first  made  as  being  the  seat  of  reason.  Physicians 
will  have  the  heart  to  be  the  first,  wherein  the  veines  and  arteries  are. 
Some  thinke  the  great  toe  is  framed  first,  others  the  navill". 

The  other  contributions  of  Diogenes  to  this  primitive  embryology, 
were  the  view  that  the  placenta  is  the  organ  of  foetal  nutrition,  and 
the  view  that  the  male  embryo  was  formed  in  four  months  but  the 
female  embryo  not  till  five  months  had  elapsed — a  notion  also  found 
in  Asclepiades  and  Empedocles,  as  we  have  seen.  He  also  associated 
heat  with  the  generation  of  little  animals  out  of  slime,  and  compared 
this  with  the  heat  of  the  uterus.  He  agreed  with  Empedocles  that 
the  embryo  was  not  alive.  "Diogenes  saith  that  infants  are  bred  within 
the  matrice  inanimate,  howbeit  in  heat,  whereupon  it  commeth  that 
naturall  heat,  so  soon  as  ever  the  infant  is  turned  out  of  the  mother's 
wombe,  is  drawen  into  the  lungs."  But  the  principal  pre-Socratic 
embryologist  was,  as  Zeller  points  out,  Alcmaeon  of  Croton,  who 
lived  in  the  sixth  century  B.C.,  a  disciple  of  Pythagoras,  though  ap- 
parently an  independent  one.  He  is  said  to  have  been  the  first  man 
to  make  dissections.  The  fragments  of  Alcmaeon  (who  is  not  to  be 
confused  with  Alcman,  the  Lacedaemonian  poet)  have  been  col- 
lected together  by  Wachtler;  the  most  important  are  xviii  and  xix. 
Athenaeus  in  the  Deipnosophists  says,  in  his  usual  chatty  way,  "Now 
with  respect  to  eggs  Anaxagoras  in  his  book  on  natural  philosophy 
says  that  what  is  called  the  milk  of  the  bird  is  the  white  which  is  in 
the  eggs".  This  may  be  a  wrong  ascription;  it  may  refer  to  Alcmaeon, 
for  Aristotle  says  in  his  book  on  the  generation  of  animals,  "Nature 
not  only  places  the  material  of  the  creature  in  the  egg  but  also  the 
nourishment  sufficient  for  its  growth,  for  since  the  mother-bird  cannot 
protect  the  young  within  herself  she  produces  the  nourishment  in  the 
egg  along  with  it.  Whereas  the  nourishment  which  is  called  milk 


is  produced  for  the  young  of  vivipara  in  another  part,  in  the  breasts, 
Nature  does  this  for  birds  in  the  egg.  The  opposite,  however,  is  the 
case  to  what  people  think  and  what  is  asserted  by  Alcmaeoii  of 
Croton.  For  it  is  not  the  white  that  is  the  milk,  but  the  yolk,  for  it 
is  this  that  is  the  nourishment  of  the  chick,  whereas  they  think  it  is 
the  white  because  of  the  similarity  of  the  colour".  Whether  Aristotle 
was  led  to  this  conclusion  because  of  his  erroneous  ideas  about  the 
part  played  in  foetal  nutrition  by  yolk  and  white  respectively  or 
whether  he  recognised  a  similarity  between  yolk  and  milk  on  account 
of  their  fatty  nature,  we  cannot  tell.  In  any  case,  his  correction  of 
Alcmaeon  was  in  the  right  direction,  and  it  is  interesting  to  compare 
the  amino-acid  distribution  in  the  casein  of  milk  and  the  vitellin  of 
yolk,  as  has  been  done  by  Abderhalden  &  Hunter  (see  p.  261). 

Parmenides  asserted  a  connection  between  male  embryos  and  the 
right  side  of  the  body  and  between  female  embryos  and  the  left  side 
of  the  body — an  idea  which,  considering  its  total  lack  of  foundation, 
has  had  a  very  long  lease  of  life  in  the  world  of  thought.  There  was 
much  controversy  on  the  question  of  how  foetal  nutrition  went  on ; 
the  atomists,  Democritus  (born  about  460  b.c.)  and  Epicurus  (born 
about  342  B.C.),  said  that  the  embryo  ate  and  drank/>^r  0^.  "Democritus 
and  Epicurus  hold",  says  Plutarch,  "that  this  unperfect  fruit  of  the 
wombe  receiveth  nourishment  at  the  mouth;  and  thereupon  it  com- 
meth  that  so  soon  as  ever  it  is  borne  it  seeketh  and  nuzzeleth  with  the 
mouth  for  the  brest  head  or  nipple  of  the  pappe :  for  that  within  the 
matrice  there  be  certain  teats;  yea,  and  mouths  too,  whereby  they 
may  be  nourished.  But  Alcmaeon  affirmeth  that  the  infant  within 
the  mother's  wombe,  feedeth  by  the  whole  body  throughout  for  that 
it  sucketh  to  it  and  draweth  in  maner  of  a  spunge,  of  all  the  food, 
that  which  is  good  for  nourishment."  It  would  appear  also  that 
Democritus  believed  the  external  form  of  the  embryo  to  be  developed 
before  the  internal  organs  were  formed. 

1-3.    Hippocrates:  the  Beginning  of  Observation 

But  the  foregoing  fragments  of  speculation  do  not  really  amount 
to  much.  The  first  detailed  and  clear-cut  body  of  embryological 
knowledge  is  associated  with  the  name  of  Hippocrates,  of  whom 
nothing  certain  is  known  save  that  he  was  born  probably  in  the 
forty-fifth  Olympiad,  about  460  b.c,  that  he  lived  on  the  island  of 
Cos  in  the  Aegean  Sea,  and  that  he  acquired  greater  fame  as  a 


physician  than  any  of  his  predecessors,  if  we  may  except  the  legendary 
names  of  Aesculapius,  Machaon  and  Podalirius.  It  has  not  been 
believed  for  many  centuries  past  that  all  the  writings  in  the  collection 
of  Hippocratic  books  were  actually  set  down  by  him,  and  much 
discussion  has  taken  place  about  the  authenticity  of  individual 

Most  of  the  embryological  information  is  contained  in  a  section 
which  in  other  respects  (style,  etc.)  shows  homogeneity.  We  are  there- 
fore rather  interested  in  that  unknown  biological  thinker  who  wrote 
the  books  in  this  class,  for  he  could  with  considerable  justice  be 
referred  to  as  the  first  embryologist.  Littre  discusses  his  identity, 
but  there  is  no  good  evidence  for  any  of  the  theories  about  it,  though 
perhaps  the  most  likely  one  is  that  he  was  Polybus,  the  son-in-law  of 
Hippocrates.  That  the  writings  on  generation  are  only  slightly  later 
than  the  time  of  Hippocrates  is  more  or  less  clear  from  the  fact  that 
Bacchius  knew  of  them,  and  actually  mentions  them. 

For  the  most  part  the  embryological  knowledge  of  Hippocrates  is 
concerned  with  obstetrical  and  gynaecological  problems.  Thus  in  the 
Aphorisms,  d(f)opicr/iioi,  the  books  on  epidemics,  eirchrifxiai,  the  treatise 
on  the  nature  of  women,  irepl  rywaLKelr)'?  (f)V(rio'?,  the  discussions  of  pre- 
mature birth,  Trepl  eirraixrjvov,  the  books  on  the  diseases  of  women, 
irepl  'yvvaixeiaiv,  and  the  pamphlet  on  superfoetation,  there  are  many 
facts  recorded  about  the  embryo,  but  all  with  obstetrical  reference. 
There  are  some  curious  notions  to  be  found  there,  such  as  the  asso- 
ciation of  right  and  left  breasts  with  twin  embryos  and  a  prognostic 
dependent  on  this. 

But  the  three  books  which  are  most  important  in  the  history  of 
embryology  are  the  treatise  on  Regimen,  irepl  StaLTr}<;,  the  work  on 
generation,  irepl  jovr]<;,  and  the  book  about  the  nature  of  the  infant, 
Trepl  ^vaio<;  TraiZiov.  The  two  latter  really  form  one  continuous 
discussion,  and  it  is  not  at  all  clear  how  they  came  to  be  split  up 
into  separate  books.  In  the  Regimen  the  writer  expounds  his  funda- 
mental physiological  ideas,  involving  the  two  main  constituents  of  all 
natural  bodies,  fire  and  water.  Each  of  these  is  made  up  of  three 
primary  natures,  only  separable  in  thought  and  never  found  isolated, 
heat,  dryness  and  moisture,  and  each  of  them  has  the  power  of 
attracting,  eXKeiv,  their  like,  an  important  feature  of  the  system.  Life 
consists  in  moisture  being  dried  up  by  fire  and  fire  being  wetted  by 
moisture  alternately,  rpo^-i'i,  the  nourishment  (moisture)  coming  into 


the  body,  is  consumed  by  the  fire  so  that  fresh  rpocfir]  is  in  its  turn 

It  is  important  to  note  that  the  Hippocratic  school  was  far  more 
akin  in  its  general  attitude  to  living  things  to  modern  physiology 
than  the  Aristotelian  and  Galenic  physiology.  For  no  considerations 
of  final  causes  complicate  the  causal  explanations  of  the  Hippocratic 
school,  and  the  author  of  the  irepl  SmtV?/?  indeed  devotes  seven  chapters 
to  a  detailed  comparison  of  the  processes  of  the  body  {a)  with  the 
processes  of  the  inorganic  world  both  celestial  and  terrestrial,  and 
(b)  with  the  processes  used  by  men  in  the  arts  and  crafts,  such  as 
iron-workers,  cobblers,  carpenters  and  confectioners.  These  dis- 
cussions present  distinct  mechanistic  features. 

He  then  in  Section  9  sets  forth  his  theory  of  the  formation  of  the 
embryo.  "Whatever  may  be  the  sex",  he  says,  "which  chance  gives 
to  the  embryo,  it  is  set  in  motion,  being  humid,  by  fire,  and  thus  it 
extracts  its  nourishment  from  the  food  and  breath  introduced  into 
the  mother.  First  of  all  this  attraction  is  the  same  throughout  because 
the  body  is  porous  but  by  the  motion  and  the  fire  it  dries  up  and 
solidifies — vtto  Be  r?)?  Kivijcno^;  Koi  tov  irvpoii  ^rfpaiveTai  koI  arepeovraL 
— as  it  solidifies,  a  dense  outer  crust  is  formed,  and  then  the  fire  inside 
cannot  any  more  draw  in  sufficient  nourishment  and  does  not  expel  the 
air  because  of  the  density  of  the  surrounding  surface.  It  therefore  con- 
sumes the  interior  humidity.  In  this  way  parts  naturally  solid  being  up 
to  a  point  hard  and  dry  are  not  consumed  to  feed  the  fire  but  fortify 
and  condense  themselves  the  more  the  humidity  disappears — these 
are  called  bones  and  nerves.  The  fire  burns  up  the  mixed  humidity 
and  forwards  development  towards  the  natural  disposition  of  the 
body  in  this  manner ;  through  the  solid  and  dry  parts  it  cannot  make 
permanent  channels  but  it  can  do  so  through  the  soft  wet  parts,  for 
these  are  all  nourishment  to  it.  There  is  also  in  these  parts  a  certain 
dryness  which  the  fire  does  not  consume,  and  they  become  compacted 
one  to  another.  Therefore  the  most  interior  fire,  being  closed  round 
on  all  sides,  becomes  the  most  abundant  and  makes  the  most  canals 
for  itself  (for  that  was  the  wettest  part)  and  this  is  called  the  belly. 
Issuing  out  from  thence,  and  finding  no  nourishment  outside,  it 
makes  the  air  pipes  and  those  for  conducting  and  distributing  food. 
As  for  the  enclosed  fire,  it  makes  three  circulations  in  the  body  and 
what  were  the  most  humid  parts  become  the  venae  cavae.  In  the 
intermediate  part  the  remainder  of  the  water  contracts  and  hardens 


forming  the  flesh."  In  this  account  of  the  formation  of  the  embryo, 
which  seems  at  first  sight  a  Httle  fantastic,  there  are  several  interesting 
things  to  be  remarked.  Firstly,  there  is  to  be  noted  throughout  it  a 
remarkable  attempt  at  causal  explanations  and  not  simply  morpho- 
logical description.  The  Hippocratic  writer  is  out  to  explain  the 
development  of  the  embryo  from  the  very  beginning  on  machine-like 
principles,  no  doubt  unduly  simplified,  but  related  directly  to  the 
observed  properties  of  fire  and  water.  In  this  way  he  is  the  spiritual 
ancestor  of  Gassendi  and  Descartes.  The  second  point  of  interest  is 
that  he  speaks  of  the  embryo  drying  up  during  its  development,  a 
piece  of  observation  which  anyone  could  make  by  comparing  a 
fourth-day  chick  with  a  fourteenth-day  one,  and  which  we  express 
to-day  in  graphical  form  (see  Fig.  220).  Thirdly,  the  ascription  of  the 
main  driving  force  in  development  to  fire  has  doubtless  no  direct 
relation  to  John  Mayow's  discovery,  two  thousand  years  later,  that 
there  is  a  similarity  between  a  burning  candle  and  a  living  mouse 
each  in  its  bell-jar,  and  may  mean  as  much  or  as  little  as  Sir  Thomas 
Browne's  remark,  "Life  is  a  pure  flame,  and  we  live  by  an  invisible 
sun  within  us".  Yet  the  essential  chemical  aspect  of  living  matter 
is  oxidation,  and  the  development  of  the  embryo  no  less  than  the 
life  of  the  adult  is  subject  to  this  rule,  so  that  what  may  have  been 
a  mere  guess  on  the  part  of  the  Hippocratic  writer,  may  also  have 
been  a  flash  of  insight  due  to  the  simple  observation  which,  after  all, 
it  was  always  possible  to  make,  namely,  that  both  fires  and  li\dng 
things  could  be  easily  stifled. 

Preformationism  is  perhaps  foreshadowed  in  Section  26  of  the 
same  treatise.  "Everything  in  the  embryo  is  formed  simultaneously. 
All  the  limbs  separate  themselves  at  the  same  time  and  so  grow,  none 
comes  before  or  after  other,  but  those  which  are  naturally  bigger 
appear  before  the  smaller,  without  being  formed  earlier.  Not  all 
embryos  form  themselves  in  an  equal  time  but  some  earlier  and  some 
later  according  to  whether  they  meet  with  fire  and  food,  some  have 
everything  visible  in  40  days,  others  in  2  months,  3,  or  4.  They 
also  become  visible  at  variable  times  and  show  themselves  to  the 
light  having  the  blend  (of  fire  and  water)  which  they  always  will 

The  work  on  Generation  is  equally  interesting.  The  earlier  sections 
deal  with  the  differences  between  the  male  and  the  female  seed,  and 
the  latter  is  identified  with  the  vaginal  secretion.  Purely  embryological 


discussion  begins  at  Section  14,  where  it  is  stated  that  the  embryo  is 
nourished  by  maternal  blood,  which  flows  to  the  foetus  and  there 
coagulates,  forming  the  embryonic  flesh.  The  proof  alleged  for  this  is 
that  during  pregnancy  the  flow  of  menstrual  blood  ceases;  therefore 
it  must  be  used  up  on  the  way  out.  In  Section  15  the  umbiHcal  cord 
is  recognised  as  the  means  by  which  foetal  respiration  is  carried  on. 
Section  1 7  contains  a  fine  description  of  development  with  a  very 
interesting  analogy.  "The  flesh",  it  is  said,  "brought  together  by  the 
spirit,  TO  TTvevfia,  grows  and  divides  itself  into  members,  hke  going  to 
like,  dense  to  dense,  flabby  to  flabby,  humid  to  humid.  The  bones 
harden,  coagulated  by  the  heat."  Then  a  demonstration  experiment 
follows :  "Attach  a  tube  to  an  earthen  vessel,  introduce  through  it  some 
earth,  sand,  and  lead  chips,  then  pour  in  some  water  and  blow  through 
the  tube.  First  of  all,  everything  will  be  mixed  up,  but  after  a  certain 
time  the  lead  will  go  to  the  lead,  the  sand  to  the  sand,  and  the  earth 
to  the  earth,  and  if  the  water  be  allowed  to  dry  up  and  the  vessel 
be  broken,  it  will  be  seen  that  this  is  so.  In  the  same  way  seed  and 
flesh  articulate  themselves.  I  shall  say  no  more  on  this  point". 
Here  again  was  an  attempt  at  causal  explanation,  rather  than 
morphological  description,  in  complete  contrast  to  the  later  work  of 


Section  22  contains  a  suggestive  comparison  between  seeds  of 
plants  and  embryos  of  animals,  but  the  identification  of  stalk  with 
umbihcal  cord  leads  to  a  certain  confusion.  Perhaps  the  most  inter- 
esting passage  of  aU  is  to  be  found  in  Section  29.  "Now  I  shall  speak", 
says  the  unknown  Hippocratic  embryologist,  "of  the  characters 
which  I  promised  above  to  discuss  and  which  show  as  clearly  as 
human  intelligence  can  to  anyone  who  will  examine  these  things 
that  the  seed  is  in  a  membrane,  that  the  umbilicus  occupies  the 
middle  of  it,  that  it  alternately  draws  the  air  through  itself  and  then 
expels  it,  and  that  the  members  are  attached  to  the  umbilicus.  In  a 
word,  all  the  constitution  of  the  foetus  as  I  have  described  it  to  you, 
you  will  find  from  one  end  to  the  other  if  you  wiU  use  the  following 
proof  Take  20  eggs  or  more  and  give  them  to  2  or  3  hens  to  incubate, 
then  each  day  from  the  second  onwards  tiU  the  time  of  hatching, 
take  out  an  egg,  break  it,  and  examine  it.  You  will  find  everything 
as  I  say  in  so  far  as  a  bird  can  resemble  a  man.  He  who  has  not 
made  these  observations  before  will  be  amazed  to  find  an  umbihcus 
in  a  bird's  egg.    But  these  things  are  so,  and  this  is  what  I  intended 


to  say  about  them."  We  see  here  as  clearly  as  possible  the  beginnings 
of  systematic  embryological  knowledge,  and  from  this  point  onwards, 
through  Aristotle,  Leonardo,  Harvey  and  von  Baer,  to  the  current 
number  of  the  Archivf.  Entwicklungsmechanik,  the  line  runs  as  straight 
as  Watling  Street. 

In  Section  30  there  is  an  important  passage  in  which  the  author 
discusses  the  phenomena  of  birth.  "I  say",  he  says,  "that  it  is  the 
lack  of  food  which  leads  to  birth,  unless  any  violence  has  been  done; 
the  proof  of  which  is  this ; — the  bird  is  formed  thus  from  the  yolk 
of  the  egg,  the  egg  gets  hot  under  the  sitting  hen  and  that  which  is 
inside  is  put  into  movement.  Heated,  that  which  is  inside  begins  to 
have  breath  and  draws  by  counter-attraction  another  cold  breath 
coming  from  the  outside  air  and  traversing  the  egg,  for  the  egg  is 
soft  enough  to  allow  a  sufficient  quantity  of  respiration  to  penetrate 
to  the  contents.  The  bird  grows  inside  the  egg  and  articulates  itself 
exactly  like  the  child,  as  I  have  previously  described.  It  comes  from 
the  yolk  but  it  has  its  food  from,  and  its  growth  in,  the  white.  To 
convince  oneself  of  this  it  is  only  necessary  to  observe  it  attentively. 
When  there  is  no  more  food  for  the  young  one  in  the  egg  and  it  has 
nothing  on  which  to  live,  it  makes  violent  movements,  searches  for 
food,  and  breaks  the  membranes.  The  mother,  perceiving  that  the 
embryo  is  vigorously  moving,  smashes  the  shell.  This  occurs  after 
20  days.  It  is  evident  that  this  is  how  things  happen,  for  when  the 
mother  breaks  the  shell  there  is  only  an  insignificant  quantity  of 
liquid  in  it.  All  has  been  consumed  by  the  foetus.  In  just  the  same 
way,  when  the  child  has  grown  big  and  the  mother  cannot  continue 
to  provide  him  with  enough  nourishment,  he  becomes  agitated, 
breaks  through  the  membranes  and  incontinently  passes  out  into  the 
external  world  free  from  any  bonds.  In  the  same  way  among  beasts 
and  savage  animals  birth  occurs  at  a  time  fixed  for  each  species 
without  overshooting  it,  for  necessarily  in  each  case  there  must  be 
a  point  at  which  intra-uterine  nourishment  will  become  inadequate. 
Those  which  have  least  food  for  the  foetus  come  quickest  to  birth 
and  vice  versa.  That  is  all  that  I  had  to  say  upon  this  subject." 

The  theory  underlying  this  passage  evidently  is  that  the  main  food 
of  the  fowl  embryo  is  the  white  and  that  the  yolk  is  there  purely  for 
constructional  purposes.  Had  the  author  not  been  strongly  attached 
to  this  erroneous  view  he  could  not  have  failed  to  notice  the  un- 
absorbed  yolk-sac  which  still  protrudes  from  the  abdomen  of  the 


hatching  chick,  and  if  he  had  given  this  fact  a  little  more  prominence 
he  could  hardly  have  come  to  enunciate  the  general  theory  of 
birth  which  appears  in  the  above  passage.  Moreover,  had  he  been 
acquainted  with  the  circulation  of  the  maternal  and  foetal  blood  in 
viviparous  animals,  he  could  hardly  have  held  that  there  was  less 
food  in  a  given  amount  of  maternal  blood  at  the  end  of  development 
than  at  the  beginning.  At  any  rate,  his  attempted  theory  of  birth 
was  a  worthy  piece  of  scientific  effort,  and  we  cannot  at  the  present 
moment  be  said  to  understand  fully  the  principles  governing  incuba- 
tion time  (see  p.  470). 

The  treatises  on  food  and  on  flesh,  trepl  Tpo(f>rj<i  and  irepl  aapKcovy 
are  both  late  additions  to  the  Hippocratic  corpus,  but  contain  points 
of  embryological  interest.  Section  30  of  the  former  contains  some 
remarks  on  embryonic  respiration,  and  Section  3  of  the  latter  has  a 
theory  of  formation  of  nerves,  bones,  etc.  by  difference  of  composition 
of  glutinous  substances,  fats,  water,  etc.  Section  6  supports  the  view 
that  the  embryo  is  nourished  in  utero  by  sucking  blood  from  the 
placenta,  and  the  proof  given  is  that  its  intestine  contains  the 
meconium  at  birth.  Moreover,  it  is  argued,  if  this  were  not  so,  how 
could  the  embryo  know  how  to  suck  after  it  is  born? 

1-4.    Aristotle 

After  the  Hippocratic  writings  nothing  is  of  importance  for  our 
subject  till  Aristotle.  It  is  true  that  in  the  Timaeus  Plato  deals  with 
natural  phenomena,  eclectically  adopting  opinions  from  many  pre- 
vious writers  and  welding  them  into  a  not  very  harmonious  or  logical 
whole.  But  he  has  hardly  any  observations  about  the  development 
of  the  embryo.  The  four  elements,  earth,  fire,  air,  and  water,  are, 
according  to  him,  all  bodies  and  therefore  have  plane  surfaces  which 
are  composed  of  triangles.  Applying  this  semi-atomistic  hypothesis 
to  the  growth  of  the  young  animal,  he  says,  "The  frame  of  the  entire 
creature  when  young  has  the  triangles  of  each  kind  new  and  may 
be  compared  to  the  keel  of  a  vessel  that  is  just  ofT  the  stocks  ;^  they 
are  locked  firmly  together  and  yet  the  whole  mass  is  soft  and  delicate, 
being  freshly  formed  of  marrow  and  nurtured  on  milk.  Now  when 
the  triangles  out  of  which  meats  and  drinks  are  composed  come  in 
from  without,  and  are  comprehended  in  the  body,  being  older  and 
weaker  than  the  triangles  already  there,  the  frame  of  the  body  gets 
the  better  of  them  and  its  newer  triangles  cut  them  up  and  so  the 


animal  grows  great,  being  nourished  by  a  multitude  of  similar 
particles."  This  is  as  near  as  Plato  gets  to  embryological  speculation. 
His  description  has  a  causal  ring  about  it,  which  is  in  some  contrast 
with  the  predominantly  teleological  tone  of  the  rest  of  his  writings ; 
for  instance,  only  a  few  pages  earlier  he  has  been  speaking  of  the 
hair  as  having  been  arranged  by  God  as  "a  shade  in  summer  and  a 
shelter  in  winter".  It  is  also  true  that  Plato  may  have  said  more 
about  the  embryo  than  appears  in  the  dialogues.  Plutarch  mentions 
various  speculations  about  sterility,  and  adds,  "Plato  directly  pro- 
nounceth  that  the  foetus  is  a  living  creature,  for  that  it  moveth  and 
is  fed  within  the  bellie  of  the  mother". 

But  all  this  was  only  the  slightest  prelude  to  the  work  of  Plato's 
pupil,  Aristotle.  Aristotle's  main  embryological  book  was  that 
entitled  Trepl  ^mcov  yeveaeco'i,  On  the  Generation  of  Animals,  but  embryo- 
logical data  appear  in  irepl  ^axop,  The  History  of  Animals,  irepl  ^wmv 
fjLopicov,  On  the  Parts  of  Animals,  Trepl  dva7rvofj<i,  On  Respiration,  and 
Trepl  ^Mcov  Ktvrjcr€(o<i,  On  the  Motion  of  Animals.  All  these  were  written 
in  the  last  three-quarters  of  the  fourth  century  B.C. 

With  Aristotle,  general  or  comparative  biology  came  into  its  own. 
That  almost  inexhaustible  profusion  of  living  shapes  which  had  not 
attracted  the  attention  of  the  earlier  Ionian  and  Italo-Sicilian  philo- 
sophers, which  had  been  passed  over  silently  by  Socrates  and  Plato, 
intent  as  ever  upon  ethical  problems,  but  which  had  been  for  cen- 
turies the  inspiration  of  the  vase-painters  and  other  craftsmen 
{(^coypdcjioL),  was  now  for  the  first  time  exhaustively  studied  and 
reduced  to  some  sort  of  order.  The  Hippocratic  school  with  their 
"Coan  classification  of  animals",  which  Burckhardt  has  discussed, 
had  indeed  made  a  beginning,  but  no  more.  It  was  Aristotle  who 
was  the  first  curator  of  the  animal  world,  and  this  comparative  out- 
look colours  his  embryology,  giving  it,  on  the  whole,  a  morphological 
rather  than  a  physiological  character. 

The  question  of  Aristotle's  practical  achievements  in  embryology 
is  interesting,  and  has  been  discussed  by  Ogle.  There  is  no  doubt 
that  he  diligently  followed  the  advice  of  the  author  of  the  Hippocratic 
treatise  on  generation  and  opened  fowl's  eggs  at  different  stages 
during  their  development,  but  he  learnt  much  more  than  the  un- 
known Hippocratic  embryologist  did  from  them.  It  is  also  clear 
that  he  dissected  and  examined  all  kinds  of  animal  embryos,  mam- 
malian and  cold-blooded.  The  uncertain  point  is  whether  he  also 


dissected  the  human  embryo.  He  refers  in  one  place  to  an  "aborted 
embryo",  and  as  he  was  able  to  obtain  easily  all  kinds  of  animal 
embryos  without  waiting  for  a  case  of  abortion,  it  is  likely  that  this 
was  a  human  embryo.  Ogle  brings  forward  six  or  seven  passages 
which  all  contain  statements  about  human  anatomy  and  physiology 
only  to  be  explained  on  the  assumption  that  he  got  his  information 
from  the  foetus.  So  it  is  probable  that  his  knowledge  of  biology  was 
extended  to  man  in  this  way,  as  would  hardly  have  been  the  case  if 
he  had  lived  in  later  times,  when  the  theologians  of  the  Christian 
Church  had  come  to  very  definite  conclusions  about  the  sanctity  of 
foetal  as  well  as  adult  life. 

The  Trept  i^wcov  ^eveaeoo<;^  the  first  great  compendium  of  embryology 
ever  written,  is  not  a  very  well-arranged  work.  There  are  a  multitude 
of  repetitions,  and  the  order  is  haphazard,  so  that  long  digressions 
from  the  main  argument  are  common.  The  work  is  divided  into 
five  books,  of  which  the  second  is  much  the  most  important  in  the 
history  of  embryology,  though  the  first  has  also  great  interest,  and 
the  third,  fourth,  and  fifth  contain  much  embryological  matter  mixed 
up  among  points  of  generation  and  sexual  physiology. 

Book  I  begins  with  an  introduction  in  which  the  relative  significance 
of  efficient  and  final  causes  is  considered,  and  chapters  i  to  7  deal 
with  the  nature  of  maleness  and  femaleness,  the  nature  and  origin 
of  semen,  the  manner  of  copulation  in  different  animals  and  the 
forms  of  penis  and  testes  found  in  them.  Chapter  8  continues  this, 
and  describes  the  different  forms  of  uterus  in  different  animals,  speaks 
of  viviparity  and  oviparity,  mentions  the  viviparous  fishes  (the 
selachians)  and  draws  a  distinction  between  perfect  and  imperfect 
eggs.  Chapter  9  discusses  the  cetacea;  10,  eggs  in  general;  and  11 
returns  to  the  differences  between  uteri.  In  chapter  12  the  question 
is  raised  why  all  uteri  are  internal,  and  why  all  testes  are  not,  and 
in  chapter  13  the  relations  between  the  urinary  and  the  genital 
systems  are  discussed.  Copulation  now  receives  attention  again,  in 
14  with  regard  to  Crustacea,  in  15  with  regard  to  cephalopoda,  and 
in  16  with  regard  to  insecta.  After  this  point  the  argument  Hfts 
itself  on  to  a  more  theoretical  plane,  and  opens  the  question  of 
pangenesis,  into  which  it  enters  at  length  during  the  course  of 
chapters  17  and  18,  refuting  eventually  the  widely-held  view  that 
the  semen  takes  its  origin  from  all  the  parts  of  the  body  so  as  to  be 
able  to  reproduce  in  the  offspring  the  characteristics  of  the  parent. 


The  nature  of  semen  receives  a  long  discussion;  it  is  decided  at  last 
that  it  is  a  true  secretion,  and  not  a  homogeneous  natural  part  (a 
tissue)  nor  a  heterogeneous  natural  part  (an  organ)  nor  an  unnatural 
part  such  as  a  growth,  nor  mere  nutriment,  nor  yet  a  waste  product. 
It  is  here  that  the  theory  is  put  forward  that  the  semen  supplies  the 
"form"  to  the  embryo  and  whatever  the  female  produces  supplies 
the  matter  fit  for  shaping.  The  obvious  question  has  next  to  be 
answered,  what  is  it  that  the  female  supplies?  Aristotle  concludes 
in  chapters  19  and  20  that  the  female  does  not  produce  any  semen, 
as  earlier  philosophers  had  held,  but  that  the  menstrual  blood  is  the 
material  from  which  the  seminal  fluid,  in  giving  to  it  a  form,  will 
cause  the  complete  embryo  to  be  produced.  This  was  not  a  new  idea, 
but  had  already  been  suggested  by  the  author  of  the  Hippocratic 
ire  pi  yovi]^.  What  was  quite  new  here,  was  the  idea  that  the  semen 
supplied  or  determined  nothing  but  the  form.  Chapters  21  and  22 
are  rather  confused ;  they  contain  more  arguments  against  pangenesis, 
and  considerations  upon  the  contrast  between  the  active  nature  of 
the  male  and  the  passive  nature  of  the  female.  Chapter  23,  which 
closes  the  first  book,  compares  animals  to  divided  plants,  for  plants 
in  Aristotle's  view  fertilise  themselves. 

Book  II  opens  with  a  magnificent  chapter  on  the  embryological 
classification  of  animals,  showing  Aristotle,  the  systematist,  at  his 
best — his  classification  is  reproduced  in  Chart  I.  But  the  chapter 
also  includes  a  brilliant  discussion  of  epigenesis  or  preformation, 
fresh  development  or  simple  unfolding  of  pre-existent  structures, 
an  antithesis  which  Aristotle  was  the  first  to  perceive,  and  the  sub- 
sequent history  of  which  is  almost  synonymous  with  the  history  of 
embryology.  The  question  in  its  acutest  form  was  not  settled  until 
the  eighteenth  century,  but  since  then  it  has  become  clear  that 
there  were  elements  of  truth  in  the  opinion  which  was  the  less  true 
of  the  two.  Chapter  2  is  not  so  important,  though  it  has  some 
interesting  chemical  analogies;  it  compares  semen  to  a  foam,  and 
suggests  that  it  was  this  foam,  like  that  of  the  sea,  which  gave 
birth  to  the  goddess  Aphrodite^.  But  chapter  3  returns  to  the 
high  level  of  speculation  and  thought  found  in  the  opening  part  of 
the  book,  for  it  deals  with  the  degree  of  aliveness  which  the  embryo 
has  during  its  passage  through  its  developmental  stages.  Aristotle 

^  To  the  Greeks  all  natural  foams  possessed  a  generative  virtue,  and  a  Zeus  Aphrios 
was  worshipped  at  Pherae  in  Thrace. 



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does  not  here  anticipate  the  form  of  the  recapitulation  theory,  but 
he  certainly  suggests  the  essence  of  it  in  perfectly  clear  terms.  This 
chapter  has  also  an  interest  for  the  history  of  theological  embryology, 
for  its  description  of  the  entry  of  the  various  souls  into  the  embryo 
was  afterwards  made  the  basis  for  the  legal  rulings  concerning 
abortion.  This  chapter  also  discusses  embryogeny  as  a  whole,  as  does 
the  succeeding  one.  Chapter  5  is  a  digression  into  the  problem 
of  why  fertilisation  is  necessary  by  the  male,  but  it  has  also  some 
curious  speculations  as  to  what  extent  the  hen's  egg  is  alive,  if  it  is 
infertile.  The  main  thread  is  resumed  in  chapters  6  and  7,  two  very 
fine  ones,  in  which  embryogeny  and  foetal  nutrition  are  thoroughly 
dealt  with,  but  dropped  again  in  the  last  section,  chapter  8,  which 
is  devoted  to  an  explanation  of  sterility.  This  ends  the  second  book. 

The  third  book  is  chiefly  concerned  with  the  application  of  the 
general  embryological  principles  described  in  the  previous  book  to 
the  comparative  field,  and  the  fourth  book  contains  a  collection  of 
minor  items  which  Aristotle  has  not  been  able  to  speak  of  before. 

But  if  the  work  as  a  whole  tails  off  in  a  rather  unsatisfactory 
manner,  its  merits  are  such  that  this  hardly  matters.  The  extra- 
ordinary thing  is  that,  building  on  nothing  but  the  scraps  of  specula- 
tion that  had  been  made  by  the  Ionian  philosophers,  and  the 
exiguous  data  of  the  Hippocratic  school,  Aristotle  should  have  pro- 
duced, apparently  without  effort,  a  text-book  of  embryology  of 
essentially  the  same  type  as  Graham  Kerr's  or  Balfour's.  It  is  even 
very  possible  that  Aristotle  was  unacquainted  with  any  of  the  Coan 
school,  for,  though  he  often  mentions  Democritus,  Anaxagoras, 
Empedocles  and  even  Polybus,  yet  he  never  once  quotes  Hippo- 
crates, and  this  is  especially  odd,  for  Aristotle  is  known  to  have 
collected  a  large  library.  Probably  Hippocrates  was  only  known  to 
Aristotle  as  an  eminent  medical  man;  if  this  is  so,  Aristotle's  achieve- 
ments are  still  more  wonderful. 

The  depth  of  Aristotle's  insight  into  the  generation  of  animals  has 
not  been  surpassed  by  any  subsequent  embryologist,  and,  con- 
sidering the  width  of  his  other  interests,  cannot  have  been  equalled. 
At  the  same  time,  his  achievements  must  not  be  over-estimated. 
Charles  Darwin's  praise  of  him  in  his  letter  to  Ogle  (which  is  too 
well  known  to  quote)  is  not  without  all  reservations  true.  There  is 
something  to  be  said  for  Lewes  as  well  as  Piatt.  Aristotle's  con- 
clusions were  sometimes  not  warranted  by  the  facts  at  his  disposal, 


and  some  of  his  observations  were  quite  incorrect.  Moreover,  he 
stood  at  the  very  entrance  into  an  entirely  unworked  field  of  know- 
ledge ;  he  had  only  to  examine,  as  it  were,  every  animal  that  he  could 
find,  and  set  down  the  results  of  his  work,  for  nobody  had  ever  done 
it  before.  It  was  like  the  great  days  of  nineteenth-century  physiology, 
when,  as  the  saying  was,  "a  chance  cut  with  a  scalpel  might  reveal 
something  of  the  first  importance". 

As  has  already  been  said,  Aristotle  regarded  the  menstrual  blood 
as  the  material  out  of  which  the  embryo  was  made.  "That,  then,  the 
female  does  not  contribute  semen  to  generation",  says  Aristotle,  "but 
does  contribute  something,  and  that  this  is  the  matter  of  the  cata- 
menia,  or  that  which  is  analogous  to  it  in  bloodless  animals,  is  clear 
from  what  has  been  said,  and  also  from  a  general  and  abstract  survey 
of  the  question.  For  there  must  needs  be  that  which  generates  and 
that  from  which  it  generates,  even  if  these  be  one,  still  they  must 
be  distinct  in  form  and  their  essence  must  be  different;  and  in  those 
animals  that  have  these  powers  separate  in  two  sexes  the  body  and 
nature  of  the  active  and  passive  sex  also  differ.  If,  then,  the  male 
stands  for  the  effective  and  active,  and  the  female,  considered  as 
female,  for  the  passive,  it  follows  that  what  the  female  would  con- 
tribute to  the  semen  of  the  male  would  not  be  semen  but  material 
for  the  semen  to  work  upon.  This  is  just  what  we  find  to  be  the  case, 
for  the  catamenia  have  in  their  nature  an  affinity  to  the  primitive 
matter."  Thus  the  male  dynamic  element  {t6  appev  iroLn^TtKov)  gives  a 
shape  to  the  plastic  female  element  {to  OrjXv  TradrjTiKov).  Aristotle 
was  right  to  the  extent  that  the  menstrual  flow  is  associated  with 
ovulation,  but  as  he  knew  nothing  of  the  mammalian  ovum,  and 
indeed,  as  is  shown  in  his  embryological  classification,  expressly  denied 
that  there  was  such  a  thing,  his  main  menstruation  theory  is  wrong. 
Yet  it  was  not  an  illegitimate  deduction  from  the  facts  before  him. 

These  views  of  Aristotle's  about  the  contribution  of  the  female  to 
the  embryo  are  in  striking  contrast  with  certain  conceptions  of  a 
century  before  which  were  probably  generally  held  in  Greece.  There 
is  a  most  interesting  passage  relating  to  them  in  the  Eumenides  of 
Aeschylus,  when,  during  the  trial  scene,  Apollo,  defending  Orestes 
from  the  charge  of  matricide,  brings  forward  a  physiological  argu- 
ment. "The  mother  of  what  is  called  her  child",  Apollo  is  made  to 
say,  "is  no  parent  of  it,  but  nurse  only  of  the  young  Hfe  that  is  sown 
in  her  (jpo(f)6<;  8e  Kv^iajo<i  veoairopov).  The  parent  is  the  male,  and 


she  but  a  stranger,  a  friend,  who,  if  fate  spares  his  plant,  preserves  it 
till  it  puts  forth." 

There  is  evidence  that  this  doctrine  was  of  Egyptian  origin,  for 
Diodorus  Siculus  says,  "The  Egyptians  hold  the  father  alone  to  be 
the  author  of  generation,  and  the  mother  only  to  provide  a  nidus 
and  nourishment  for  the  foetus".  Whether  this  was  so  or  not,  the 
influence  of  such  a  doctrine  must  have  been  tremendous.  We  know 
that  the  conception  of  the  female  sex  as  playing  the  part  of  farm-land, 
i.e.  of  woman  as  a  field  in  which  grain  was  sown,  was  widespread 
in  antiquity;  Hartland  and  S.  A.  Cook  have  collected  examples  of 
it  from  Vedic,  Egyptian  and  Talmudic  sources.  A  late  echo  of  it  is 
to  be  found  in  Lucretius,  where  he  refers  to  "Venus  sowing  the  field 
of  woman" — 

atque  in  eost  Venus  ut  muliebria  conserat  arva. 

Nor  would  resemblances  between  mothers  and  children  suffice  to 
kill  this  belief,  for  plants  may  diflfer  slightly  according  to  the  soil 
in  which  they  are  planted.  Such  an  idea  would  be  the  natural 
foundation  for  the  practice — also  widespread  in  antiquity — of  putting 
captured  males  to  death,  and  retaining  the  females  as  concubines. 
On  such  a  theory  no  fear  would  be  entertained  of  corrupting  the 
race  with  alien  blood  in  this  way.  The  whole  matter  affords  an 
excellent  illustration  of  the  way  in  which  an  apparently  academic 
theory  may  have  the  most  far-reaching  effects  on  social  and  political 
events,  and  Aristotle,  far  from  being  remote  from  practical  affairs 
as  he  examined  his  viviparous  fishes  and  made  marginal  notes  on 
his  copy  of  Empedocles,  is  seen  to  be  labouring  at  their  very  root. 

The  embryo,  then,  took  its  origin  from  the  menstrual  blood,  on 
which,  and  in  which,  the  seminal  essence  operated  to  produce  it. 
But  the  perplexing  question  of  the  order  of  formation  of  the  parts 
remained  unsettled,  though  it  had  already  been  opened  by  earlier 
thinkers.  What  they  had  not  done  was  to  put  the  question,  as  it 
were,  into  the  form  of  a  motion ;  they  had  not  grasped  the  existence 
of  two  main  alternatives,  one  of  which  would  have  to  be  chosen 
before  any  further  progress  could  be  made.  This  is  just  what  Aristotle 
did.  "There  is  considerable  difficulty",  says  he,  "in  understanding 
how  the  plant  is  formed  out  of  the  seed  or  any  animal  out  of  the 
semen.  Everything  that  comes  into  being  or  is  made  must  (i)  be 
made  out  of  something,  (2)  be  made  by  the  agency  of  something, 


and  (3)  must  become  something.  Now  that  out  of  which  it  is  made 
is  the  material;  this  some  animals  have  in  its  first  form  within  them- 
selves, taking  it  from  the  female  parent,  as  all  those  which  are  not 
born  aHve  but  produced  as  a  scolex  or  egg;  others  receive  it  for  a 
long  time  from  the  mother  by  sucking,  as  the  young  of  all  those 
which  are  not  only  externally  but  also  internally  viviparous.  Such 
is  the  material  out  of  which  things  come  into  being,  but  we  now 
are  enquiring  not  out  of  what  the  parts  of  an  animal  are  made,  but 
by  what  agency.  Either  it  is  something  external  which  makes  them 
or  else  it  is  something  existing  in  the  seminal  fluid  and  the  semen; 
and  this  must  either  be  soul  or  a  part  of  a  soul,  or  something  con- 
taining soul."  Aristotle  concludes  that  there  is  no  external  shaping 
influence,  but  only  something  or  other  contained  in  the  embryo  itself. 
To  this  extent  he  was  wrong,  for  the  influence  of  the  proper  physico- 
chemical  environment  on  the  growing  embryo  is  as  important  as  its 
physico-chemical  internal  constitution  (later  he  modified  his  views 
on  this).  But  now  he  goes  on  to  deal  with  the  main  question,  and 
says,  "How  then  does  it  (the  shaping  influence)  make  the  other  parts? 
All  the  parts,  as  heart,  lung,  liver,  eye,  and  all  the  rest,  come  into 
being  either  together  or  in  succession,  as  is  said  in  the  verse  ascribed 
to  Orpheus,  for  there  he  says  that  an  animal  comes  into  being  in 
the  same  way  as  the  knitting  of  a  net.  That  the  former  is  not  the 
fact  is  plain  even  to  the  senses,  for  some  of  the  parts  are  clearly 
visible  as  already  existing  in  the  embryo  wliile  others  are  not;  that 
it  is  not  because  of  their  being  too  smaU  that  they  are  not  visible  is 
clear,  for  the  lung  is  of  greater  size  than  the  heart,  and  yet  appears 
later  than  the  heart  in  the  original  development".  This  passage 
demonstrates  that  Aristotle  had  opened  hen's  eggs  at  different  stages, 
and  was  well  acquainted  with  the  appearances  presented  there  as 
early  as  the  third  day.  He  goes  on  to  set  forth  a  further  alternative. 
Agreeing  that  a  continuously  new  formation  of  parts  takes  place,  and 
not  merely  an  unfolding  of  parts  already  present  in  the  semen  or  the 
menstrual  blood,  is  this  brought  about  by  a  chain  of  creations  or  by 
one  original  creation?  In  other  words,  does  the  heart  come  into  being 
first,  and  then  proceed  to  form  the  liver,  and  then  the  liver  go  on 
to  form  the  lungs,  or  do  they  simply  appear  one  after  the  other  without 
such  a  creative  inter-relationship?  Aristotle  argues  against  the  former 
view  on  the  ground  that  if  one  organ  formed  another,  the  second 
one  would  have  to  resemble  the  first  in  some  way,  which  is  not  the 



case.  His  words  on  this  subject  cannot  be  condensed.  "But  neither 
can  the  (formative)  agent  be  external  and  yet  it  must  needs  be  one 
or  other  of  the  two.  We  must  try  then  to  solve  this  difficulty,  for 
perhaps  some  one  of  the  statements  made  (already)  cannot  be  made 
without  qualification,  e.g.  the  statement  that  the  parts  cannot  be 
made  by  what  is  external  to  the  semen.  For  if  in  a  certain  sense  they 
cannot,  yet  in  another  sense  they  can."  (Thus  Aristotle  does  some 
justice  to  the  environment.)  "It  is  possible,  then,  that  A  should 
miove  B  and  B  should  move  C,  that,  in  fact,  the  case  should  be  the 
same  as  with  the  automatic  machines  shown  as  curiosities.  For  the 
parts  of  such  machines  while  at  rest  have  a  sort  of  potentiality  of 
motion  in  them,  and  when  any  external  force  puts  the  first  of  them 
into  motion,  immediately  the  next  is  moved  in  actuality.  As,  then, 
in  these  automatic  machines  the  external  force  moves  the  parts  in 
a  certain  sense  (not  by  touching  any  part  at  the  moment  but  by 
having  touched  one  previously) ,  in  like  manner  also  that  from  which 
the  semen  comes  or  in  other  words  that  which  made  the  semen,  sets 
up  the  movement  in  the  embryo  and  makes  the  parts  of  it  by  having 
touched  first  something  though  not  continuing  to  touch  it.  In  a  way 
it  is  the  innate  motion  that  does  this,  as  the  act  of  building  builds 
a  house.  Plainly,  then,  while  there  is  something  which  makes  the 
parts,  this  does  not  exist  as  a  definite  object,  nor  does  it  exist  in  the 
semen  at  the  first  as  a  complete  part."  This  notion  of  the  setting 
in  motion  of  a  wound-up  clock  is  substantially  modern  and  underlies 
the  physico-chemical  analysis  of  the  developing  embryo.  It  is  really 
striking  to  find  Aristotle  using  the  machine  analogy  in  order  to  explain 
himself,  for  he,  of  all  biologists,  emphasised  the  final  cause  in  natural 
operations.  However,  he  soon  returns  to  a  more  vitalistic  attitude 
in  the  succeeding  section.  "But  how  is  each  part  formed?"  he  says. 
"We  must  answer  this  by  starting  in  the  first  instance  from  the 
principle  that,  in  all  products  of  Nature  or  art,  a  thing  is  made  by 
something  actually  existing  out  of  that  which  is  potentially  the  same 
as  the  finished  product.  Now  the  semen  is  of  such  a  nature  and  has 
in  it  such  a  principle  of  motion,  that  when  the  motion  is  ceasing 
each  of  the  parts  comes  into  being  and  that  as  a  part  having  life  or 
soul. . .  .And  just  as  we  should  not  say  that  an  axe  or  other  instrument 
or  organ  was  made  by  the  fire  alone,  so  neither  shall  we  say  that  foot 
or  hand  were  made  by  fire  alone .  . .  .While,  then,  we  may  allow  that 
hardness  and  softness,  stickiness  and  brittleness,  and  whatever  other 


qualities  are  found  in  the  parts  that  have  life  and  soul,  may  be  caused 
by  mere  heat  and  cold  yet,  when  we  come  to  the  principle,  Xoyof, 
in  virtue  of  which  flesh  is  flesh  and  bone  is  bone,  that  is  no  longer  so ; 
what  makes  them  is  the  movement  set  up  by  the  male  parent,  who 
is  in  actuality  what  that  out  of  which  the  offspring  is  made  is  in 
potentiaUty .  This  is  what  we  find  in  the  products  of  art ;  heat  and 
cold  may  make  the  iron  soft  or  hard,  but  what  makes  a  sword  is  the 
movement  of  the  tools  employed,  this  movement  containing  the 
principle  of  the  art.  For  the  art  is  the  starting-point  and  form  of 
the  product;  only  it  exists  in  something  else  (i.e.  potentially  in  the 
mind  of  the  artist),  whereas  the  movement  of  nature  exists  in  the 
product  itself,  issuing  from  another  Nature  (i.e.  the  parent)  which 
has  the  form  in  actuaHty." 

Thus  Aristotle,  evidently  influenced  by  his  doctrine  of  "form"  and 
"matter",  decided  against  preformation  and  pictured  at  one  and 
the  same  time  the  unformed  catamenia  as  containing  a  kind  of  clock- 
work m.echanism  which,  once  set  in  motion,  would  inevitably  produce 
the  finished  embryo,  and  also  as  an  inchoate  substance  on  which 
the  seminal  essence  should  act  like  a  swordmaker  producing  a  sword 
according  to  the  motions  of  a  natural  art.  These  two  ideas  are  not 
completely  reconciled  in  Aristotle,  and  a  consideration  of  artificial 
fertiHsation  would  have  provided  a  test  case,  had  he  been  able  to 
know  of  the  experiments  of  Delage  and  Loeb.  For,  on  his  second 
theory,  butyric  acid  would  transmute  a  sea-urchin's  egg  into  butyric 
acid  and  not  into  a  sea-urchin:  while,  on  his  first  theory,  the  egg 
would  make  the  sea-urchin  irrespective  of  what  influence  it  was  that 
swung  the  starting-handle. 

Aristotle  has  a  good  deal  to  say  about  the  theory  of  recapitulation, 
as  it  was  afterwards  to  be  called.  He  thought  there  was  no  doubt 
that  the  vegetative  or  nutritive  soul  existed  in  the  unfertilised  material 
of  the  embryo,  "for  nobody",  as  he  says,  "would  put  down  the  un- 
fertilised embryo  as  soulless  or  in  every  sense  bereft  of  life  (since 
both  the  semen  and  the  embryo  of  an  animal  have  every  bit  as 
much  life  as  a  plant)  and  it  is  productive  up  to  a  certain  point. ...  As 
it  develops  it  also  acquires  the  sensitive  soul  in  virtue  of  which  an 
animal  is  an  animal. .  .  .  For  first  of  all  such  embryos  seem  to  live 
the  life  of  a  plant,  and  it  is  clear  that  we  must  be  guided  by  this  in 
speaking  of  the  sensitive  and  the  rational  soul.  For  all  three  kinds 
of  soul,  not  only  the  nutritive,  must  be  possessed  potentially  before 


they  are  possessed  actually".  These  passages  show  very  clearly  the 
line  of  thought  contained  in  the  recapitulation  theory,  as  do  the 
following.  "For  an  animal  does  not  become  at  the  same  time  an 
animal  and  a  man  or  a  horse  or  any  other  particular  animal",  i.e. 
the  more  general  appears  first  and  the  more  particular  later.  "For 
the  end  is  developed  last,  and  the  peculiar  character  of  the  species 
is  the  end  of  the  generation  in  each  individual",  i.e.  the  embryo 
attains  the  point  of  being  definitely  not  a  plant  before  it  attains  that 
of  being  definitely  not  a  mollusc  but  a  horse  or  a  man.  Aristotle 
concludes  that  the  diflferent  sorts  of  souls  enter  the  embryo  at  different 
stages  of  development,  just  as  the  shape  of  the  embryo  gradually 
approximates  to  whatever  adult  shape  it  is  destined  to  conform  to. 

Aristotle  continues  to  discuss  the  central  problems  of  embryology, 
but  now  in  a  way  which  presents  features  of  directly  physico-chemical 
interest.  "When  the  material  secreted  by  the  female  in  the  uterus 
has  been  fixed  by  the  semen  of  the  male  (this  acts  in  the  same  way 
as  rennet  acts  upon  milk,  for  rennet  is  a  kind  of  milk  containing  vital 
heat,  which  brings  into  one  mass  and  fixes  the  similar  material,  and 
the  relation  of  the  semen  to  the  catamenia  is  the  same,  milk  and  the 
catamenia  being  of  the  same  nature) ,  when,  I  say,  the  more  solid 
part  comes  together,  the  liquid  is  separated  off  from  it,  and  as  the 
earthy  parts  solidify,  membranes  form  all  round  it;  this  is  both  a 
necessary  result  and  for  a  final  cause,  the  former  because  the  surface 
of  the  mass  must  solidify  on  heating  as  well  as  on  cooling,  the  latter 
because  the  foetus  must  not  be  in  a  liquid  but  separated  from  it." 
Later  on,  he  also  says,  "The  reason  is  similar  to  that  of  the  growth 
of  yeast,  for  yeast  also  grows  great  from  a  small  beginning  as  the  more 
sohd  part  liquefies  and  the  liquid  is  aerated.  This  is  effected  in 
animals  by  the  nature  of  the  vital  heat,  in  yeasts  by  the  heat  of  the 
juice  contained  in  them". 

These  remarkable  passages  contain  the  first  reference  to  enzyme 
action  ever  made  in  a  discussion  on  embryology.  The  solidification  of 
the  outer  crust  is  of  course  Hippocratic,  as  we  have  already  seen.  The 
part  about  the  amnios  is  unfortunate ;  for  the  facts  are  exactly  contrary. 

"The  heart  is  first  differentiated",  says  Aristotle,  "as  is  clear  not 
only  to  the  senses  (for  it  is  so)  but  on  theoretical  grounds.  For  when- 
ever the  young  animal  has  been  separated  from  both  parents  it  must 
be  able  to  manage  itself,  like  a  son  who  has  set  up  house  away  from 
his  father."    This  is  good  observation.  "The  heart  is  the  principle 


and  origin  of  the  embryo",  says  Aristotle.  This  conception  of  cor 
primum  vivens,  ultimum  moriens  (a  phrase  never  used  by  Aristotle 
himself),  has  henceforward  a  long  and  tortuous  history,  which  has 
been  described  by  Ebstein  and  others. 

Aristotle  goes  on  to  describe  the  membranes  of  the  mammalian 
foetus  with  its  umbilical  cord:  "The  vessels  join  on  to  the  uterus 
like  the  roots  of  plants  and  through  them  the  embryo  receives  its 
nourishment.  This  is  why  the  embryo  remains  in  the  uterus";  not 
as  Democritus  thought,  so  that  it  might  be  moulded  into  the  maternal 
shape.  The  embryo  "straightway  sends  off  the  cord  like  a  root  to 
the  uterus  ".  He  carefully  notes,  as  if  the  conception  of  axial  gradients 
was  existing  deep  down  in  his  mind,  that  the  cephalic  parts  of  the 
embryo  are  formed  first.  "The  greater  become  visible  before  the  less ", 
he  says,  "even  if  some  of  them  do  not  come  into  being  before  them. 
First  the  parts  above  the  hypozoma"  (a  term  more  or  less  corre- 
sponding to  "diaphragm")  "are  differentiated  and  are  superior  in 
size,  the  part  below  is  both  smaller  and  less  differentiated.  This 
happens  in  all  animals  in  which  exists  the  distinction  of  upper  and 
lower,  except  in  the  insects."  Aristotle  gives  as  his  explanation  of 
this  a  teleological  argument:  "This  is  why  the  parts  about  the  head 
and  especially  the  eyes  appear  largest  in  the  embryo  at  an  early 
stage,  while  the  parts  below  the  umbilicus,  as  the  legs,  are  small; 
for  the  lower  parts  are  for  the  sake  of  the  upper  and  are  neither 
parts  of  the  end,  nor  able  to  form  it". 

Embryonic  growth  is  thus  described  by  Aristotle:  "The  homo- 
geneous parts  (tissues)  are  formed  by  heat  and  cold,  for  some  are 
put  together  and  solidified  by  the  one  and  some  by  the  other .... 
The  nutriment  oozes  through  the  blood-vessels  and  the  passages  in 
each  of  the  parts,  like  water  in  unbaked  pottery,  and  thus  is  formed 
the  flesh  or  its  analogues,  being  solidified  by  cold,  which  is  why  it 
is  dissolved  by  fire.  But  all  the  particles  given  ofT  which  are  too 
earthy,  having  but  little  moisture  and  heat,  cool  as  the  moisture 
evaporates  along  with  the  heat,  so  they  become  hard  and  earthy  in 
character,  as  nails,  horns,  hoofs,  and  beaks,  and  therefore  they  are 
softened  by  fire  but  none  of  them  is  melted  by  it,  while  some  of  them, 
as  egg-shells,  are  soluble  in  liquids.  The  sinews  and  bones  are  formed 
by  the  internal  heat  as  the  moisture  dries,  and  hence  the  bones  are 
insoluble  by  fire  like  pottery,  for  like  it  they  have  been  as  it  were 
baked  in  an  oven  by  the  heat  in  the  process  of  development. .  . .  The 


skin,  again,  is  formed  by  the  drying  of  the  flesh,  Hke  the  scum  upon 
boiled  substances;  it  is  so  formed  not  only  because  it  is  upon  the 
outside,  but  also  because  what  is  glutinous,  being  unable  to  evaporate, 
remains  on  the  surface".  Here  is  a  splendid  collection  of  mechanical 
processes,  but  Aristotle  is  careful  to  add:  "As  we  said,  all  these  things 
must  be  understood  to  be  formed  in  one  sense  of  Necessity,  but  in 
another  sense  not  of  Necessity  but  for  a  Final  Cause". 

Concurrent  growth  and  differentiation,  the  former  being  temporally 
sequent  to  the  latter,  he  thus  describes:  "The  upper  half  of  the  body, 
then,  is  first  marked  out  in  the  order  of  development ;  as  time  goes 
on  the  lower  also  reaches  its  full  size  in  the  sanguinea.  All  the  parts 
are  first  marked  out  in  their  outlines  and  acquire  later  on  their  colour 
and  softness  or  hardness,  exactly  as  if  Nature  were  a  painter  producing 
a  work  of  art,  for  painters  too  first  sketch  in  the  animal  with  lines 
and  only  after  that  put  in  the  colours".  Aristotle  had  some  difficulty 
about  the  eyes;  he  noted  that  they  were  disproportionately  large 
in  early  bird  embryos,  but  he  seems  to  have  thought  that  they  shrunk 
absolutely  as  well  as  relatively  during  further  development.  It  takes 
him  a  great  deal  of  ingenuity  to  invent  a  teleological  explanation  for 
this  quite  imaginary  fact. 

The  food  which  the  embryo  derives  from  the  mother,  according 
to  Aristotle,  is  of  two  distinct  kinds,  nutritious,  formative,  or  creative, 
TO  OpeTTTLKov,  and  that  which  is  concerned  with  simple  increase  of 
size,  TO  et?  fxeyedo';  itolovv  tijv  eirihoaiv.  This  distinction  is  difficult  to 
understand,  and,  though  it  would  be  attractive  to  interpret  the  former 
as  vitamines  and  the  latter  as  fats,  proteins  and  carbohydrates,  that 
would  probably  be  putting  too  much  of  a  strain  on  our  belief  in 
Aristotle's  insight.  He  has  much  to  say  of  the  placenta,  and  ascribes 
to  it  its  correct  function.  He  combats  the  idea  that  foetal  nutrition 
is  maintained  by  uterine  paps,  alleging  against  it  the  fact  that  all 
embryos  are  enclosed  in  membranes.  He  discusses  birds'  eggs  in 
great  detail,  referring  to  infertile  or  "wind-eggs"  and  to  the  action 
of  heat  during  incubation.  He  considered  that  the  embryo  was 
formed  from  the  white  exclusively,  and  only  got  its  nourishment 
from  the  yolk,  which  was  a  backward  step  in  view  of  what  had  already 
been  said  by  the  Hippocratic  embryologist.  He  knew  of  the  whiteness 
of  the  yolk  when  first  formed  in  the  oviduct  and  of  the  yellow  colour 
of  the  layers  of  yolk  added  to  it  in  its  passage  down  that  tube,  but 
he  held  that  the  yellow  colour  was  "sanguineous",  and  therefore  hot, 


while  the  white  was  cold.  He  held  also  that  the  bird  embryo  always 
developed  at  the  pointed  end;  no  doubt,  as  Piatt  has  suggested, 
Aristotle  belonged  to  Swift's  class  of  "Little-endians",  and  must  have 
always  opened  them  at  that  end,  in  which  case  he  would  find  the 
embryo  there,  for  the  yolk  always  swims  embryo  uppermost.  He 
knew  also  that  the  yolk  liquefied  during  the  first  week  of  develop- 
ment, and  that  it  grew  larger,  but  he  did  not  guess  the  right  reasons 
of  these  phenomena.  He  knew  the  arrangements  for  embryonic 
development  in  the  dolphins  and  ovo viviparous  sharks.  He  takes 
a  strong  line  over  spontaneous  generation;  "nothing",  he  says, 
"comes  into  being  by  putrefying,  but  by  concocting".  And  so  in 
many  other  passages  where  detailed  observation  is  joined  with  acute 
reasoning.  So  far  only  the  treatise  on  the  generation  of  animals 
has  been  under  consideration.  But  in  the  irepl  ^oiwv,  also,  there  are 
many  embryological  data,  and  it  is  strange  that  those  detailed 
observations  upon  the  developing  fowl  embryo,  which  demonstrate 
more  than  anything  else  Aristotle's  wonderful  powers  of  observation, 
are  not  contained  at  all  in  the  Generation  of  Animals,  but  in  the  History 
of  Animals.  He  takes  animals  one  by  one  in  order,  and  in  each  case 
deals  with  their  generative  peculiarities,  such  as  their  mode  of 
hatching,  their  incubation  period,  their  fertility,  etc.  For  instance, 
he  correctly  relates  how  cartilaginous  fish  embryos  possess  a  yolk-sac 
like  bird  embryos,  but  no  allantois.  In  his  account  of  the  fowl  he  is 
unusually  precise. 

Most  of  the  sixth  book  is  occupied  with  the  account  of  the  genera- 
tion of  birds  and  fishes,  and  the  seventh  treats  also  very  fully  of  that 
of  man.  But  in  both  cases  it  is  a  description  that  is  given;  more 
theoretical  considerations  are  left  to  the  book  on  generation,  and  for 
this  reason  the  latter  work  is  the  more  interesting.  From  a  general 
point  of  view  the  History  of  Animals  has  a  more  wonderful  wealth 
of  material  in  it  than  the  book  on  generation,  but,  at  the  same  time, 
it  also  indulges  in  much  more  extravagant  stories,  such  as  those  of 
the  "kindly  and  gentle  dolphin"  and  the  equine  Oedipus,  and  to 
that  extent  the  austerity  of  the  book  on  generation  charms  us  more. 

Other  treatises  also  mention  embryology.  The  irepl  ^(owv  fioployvj  On 
the  Parts  of  Animals,  has  a  passage  in  which  the  appearance  of  the 
third-day  chick  embryo  is  described,  and  refers  to  observations  on 
the  lack  of  pigment  and  of  distinct  medullary  canals  in  bones  in 
foetal  life.  The  small  work  entitled  Trepl  dvairvoTj^;,  On  Respiration,  also 

74  EMBRYOLOGY   IN  ANTIQ^UITY  [pt.  ii 

refers  to  the  heart  as  the  first  organ  to  be  formed,  and  so  as  the  seat 
of  the  soul.  But  these  minor  sources  contribute  little  to  the  progress 
of  the  science,  and  it  is  upon  the  great  work  On  the  Generation  of  Animals 
that  Aristotle's  well-deserved  fame  as  an  embryologist  will  always  rest. 

If  I  have  devoted  a  very  large  space  to  an  account  of  Aristotle's 
contributions  to  embryology,  it  is,  firstly,  because  they  are  actually 
greater  in  number  than  those  of  any  other  individual  embryologist, 
and  secondly,  because  they  had  so  profound  an  influence  upon  the 
following  twenty  centuries.  Embryology  from  the  third  century  B.C. 
to  the  seventeenth  century  a.d.  is  meaningless  unless  it  is  studied  in 
the  light  of  Aristotle. 

His  outstanding  contributions  to  embryology  may  be  put  in  the 
following  way: 

1.  He  carried  to  their  logical  conclusion  the  principles  of  the 
observation  of  facts  suggested  by  the  unknown  Hippocratic 
embryologist,  and  added  to  them  a  discipline  of  classification 
and  correlation  of  facts  which  gave  embryology  a  quite  new 

2.  He  introduced  the  comparative  method  into  embryology,  and 
by  studying  a  multitude  of  living  forms  was  able  to  lay  the 
foundation  for  future  science  of  the  various  ways  in  which 
embryonic  growth  can  take  place.  Thus  he  knew  of  oviparity, 
ovoviviparity,  and  viviparity,  and  one  of  his  distinctions  is 
substantially  the  same  as  that  known  to  modern  embryology 
between  holoblastic  and  meroblastic  yolks. 

3 .  He  distinguished  between  primary  and  secondary  sexual  charac- 

4.  He  pushed  back  the  origin  of  sex-determination  to  the  very 
beginning  of  embryonic  development. 

5.  He  associated  regeneration  phenomena  with  the  embryonic 

6.  He  reaUsed  that  the  previous  speculations  on  the  formation  of 
the  embryo  could  be  absorbed  into  the  definite  antithesis  of  pre- 
formation and  epigenesis,  and  he  decided  that  the  latter  alterna- 
tive was  the  true  one. 

7.  He  put  forward  a  conception  of  the  unfertilised  egg  as  a  com- 
plicated machine,  the  wheels  of  which  would  move  and 
perform  their  appointed  function  in  due  course  when  once  the 
master-lever  had  been  released. 


8.  He  foreshadowed  the  theory  of  recapitulation  in  his  specula- 
tions on  the  order  in  which  the  souls  came  to  inhabit  the 
embryo  during  its  growth,  and  in  his  observation  that 
universal  characteristics  precede  particular  characteristics  in 

9.  He  foreshadowed  the  theory  of  axial  gradients  by  his  observa- 
tions on  the  greater  and  more  rapid  development  of  the  cephalic 
end  in  the  embryo. 

10.  He  allotted  the  correct  functions  to  the  placenta  and  the 
umbilical  cord. 

11.  He  gave  a  description  of  embryonic  development  involv- 
ing comparison  with  the  action  of  rennet  and  yeast,  fore- 
shadowing thus  our  knowledge  of  organic  catalysts  in 

But  there  was  another  side  to  the  picture.  Aristotle  made  three 
big  mistakes,  and  here  I  do  not  refer  to  any  matters  of  detail,  in 
which  it  would  not  have  been  humanly  possible  to  be  more  than 
very  often  right,  but  rather  to  general  notions,  such  as  the  eleven 
correct  ones. 

They  were  as  follows : 

1.  He  was  incorrect  in  his  view  that  the  male  supplies  nothing 
tangible  to  the  female  in  the  process  of  fertilisation.  To  say 
that  the  semen  gave  the  "form"  to  the  inchoate  "matter"  of 
the  menstrual  blood  was  equivalent  to  saying  that  the  seminal 
fluid  carried  nothing  in  it  but  simply  an  immaterial  breath 
along  with  it.  Aristotle  did  not  envisage  the  existence  of 

2.  He  was  entirely  wrong  in  his  teaching  about  the  scolex.  The 
caterpillar  is  not,  as  he  supposed,  an  egg  laid  too  soon,  but  has 
already  passed  through  the  embryonic  state. 

3.  He  was  misled  by  some  observations  on  castrated  animals  and 
so  did  not  ascribe  to  the  testis  its  true  function. 

Such  mistakes  as  these,  however,  were  not  nearly  so  important  as 
the  solid  ground  gained  by  his  correct  answers.  They  were  always 
open  to  experimental  test,  even  though  the  authority  of  his  name 
precluded  it  until  the  Renaissance.  But  there  was  one  aspect 
of  his  embryological  work  which  was  to  exercise  an  unfortunate 
influence  on  the  subsequent  progress  of  the  science,  namely,  his  in- 
sistence on  teleological  explanations.    He  was  always  seeking  for 


final  as  well  as  efficient  causes.  "The  ancient  Nature-philosophers 
did  not  see  that  the  causes  were  numerous ;  they  only  saw  the  material 
and  efficient  causes  and  did  not  distinguish  even  these,  while  they  made 
no  enquiry  at  all  into  the  formal  and  final  causes."  "Democritus", 
he  says,  "neglecting  the  final  cause,  reduces  to  Necessity  all  the 
operations  of  Nature.  Now  they  are  necessary  it  is  true,  but  yet 
they  are  also  for  a  final  cause,  and  for  the  sake  of  what  is  best  in 
each  case." 

Now  in  Aristotle  this  was  all  to  the  good.  A  metaphysician  as  well 
as  a  scientific  worker,  he  was  able  to  use  the  concept  of  purposiveness 
as  a  heuristic  aid,  but  he  never  rested  upon  it.  The  trouble  was 
that  he  introduced  it  into  the  discussion  at  all.  It  is  an  interesting 
speculation  to  consider  what  would  have  happened  if  the  first  great 
biologist  had  not  brought  final  causes  into  his  teaching ;  perhaps  the 
subsequent  history  of  biology,  and  science  as  a  whole,  would  have 
been  very  different.  For  final  causes  irresistibly  led  to  the  theological 
blank  alleys  into  which  men's  thoughts  were  ushered  and  there  left 
to  grope  till  the  end  of  the  Middle  Ages. 

Perhaps  Aristotle  would  not  have  made  so  many  great  discoveries 
if  he  had  been  more  of  a  Democritus.  For  teleology  is,  like  other 
varieties  of  common  sense,  useful  from  time  to  time;  e.g.  Harvey  told 
Boyle  that  he  was  led  to  certain  important  considerations  by  meditat- 
ing upon  the  final  cause  of  the  valves  in  the  veins ;  and  every  biologist 
acts  in  the  same  way  at  the  present  time.  But  the  important  thing 
is  not  to  give  the  last  word  to  teleology.  And  those  attractive  shady 
places  which  Aristotle,  guided  by  his  genius,  quickly  passed  through 
on  his  perpetual  journeys  into  the  hot  sunlight  of  research  and  specu- 
lation were  so  many  traps  for  those  who  followed  him.  He  himself 
knew  how  to  change  rapidly  from  metaphysician  into  physicist  and 
back  again,  how  to  bow  politely  to  the  final  cause  and  press  on  with 
the  dissection;  but  the  later  Peripatetics  had  no  knowledge  of  this  art, 
nor  had  the  Patristic  Doctors,  nor  the  mediaeval  Aristotelians;  who 
all  remained  sleeping  quietly  in  the  shade  of  the  will  of  God.  He  knew 
very  well  from  the  sea  (to  use  Bacon's  metaphor  at  last)  the  look  of 
the  Circe  country  of  teleology,  but  he  never  visited  it  for  long  at  a 
time^  being  an  authentic  Odysseus,  unlike  so  many  later  heads,  who, 
following  the  example  of  Plato,  "anchored  upon  that  shore"  and, 
dropping  their  hooks  to  the  sound  of  plain-song,  there  rode,  never 
to  hoist  sail  again. 


1-5.    The  Hellenistic  Age 

Aristotle  died  in  322  e.g.  From  that  year  until  1534,  the  date  of 
the  birth  of  Volcher  Goiter,  first  in  time  of  the  Renaissance  embryo- 
logists,  embryology  has  very  little  history. 

The  founder  of  the  stoical  philosophy,  Zeno  of  Gitium,  was  born 
some  twenty  years  before  the  death  of  Aristotle.  "Pious  and  mag- 
nanimous as  Stoicism  was  in  the  field  of  conduct",  says  AUbutt, 
"creating  or  nourishing  that  elevation  of  mind  which  distinguished 
the  nobler  Roman  of  the  Empire,  yet  in  Rome,  as  in  England,  its 
natural  science  was  of  no  account.  The  spirit  of  it  was  indeed  rather 
alien  than  akin  to  science.  The  mind  of  the  Porch  which  called  itself 
'practical'  was  reluctant  to  all  'speculation',  natural  science  in- 
cluded." The  Stoics  regarded  the  four  quahties  of  cold,  hot,  wet, 
and  dry,  as  ultimate,  instead  of  the  earth,  fire,  air,  and  water  of  the 
Peripatetics  and  their  predecessors,  Plutarch,  in  his  summary  of 
philosophic  opinions  already  mentioned,  has  some  passages  relating 
to  their  views  on  the  development  of  the  embryo.  "The  Stoicks  say", 
he  relates,  "that  the  foetus  is  fed  by  the  fecundine  and  navell;  where- 
upon it  is  that  midwives  presently  knit  up  and  tie  the  navell  string 
fast,  but  open  the  infants  mouth,  to  the  end  that  it  be  acquainted 
with  another  kind  of  nourishment."  And  elsewhere,  "The  Stoicks 
say  that  it  is  a  part  of  the  wombe  and  not  an  animall  by  itselfe.  For 
like  as  fruits  be  parts  of  trees,  which  when  they  be  ripe  do  fall,  even 
so  it  is  with  an  infant  in  the  mother's  wombe. . . .  The  Stoicks  are 
of  opinion  that  the  most  parts  are  formed  all  at  once ;  but  Aristotle 
saith  the  backbone  and  loines  are  first  framed  like  as  the  keele  in 
a  ship."  But  to  which  of  Zeno's  successors,  Gleanthes,  Ghrysippus, 
Grates  or  the  rest,  these  sayings  are  to  be  attributed,  is  not  known. 

The  Epicureans  also  had  opinions  on  these  subjects.  They  thought 
that  the  foetus  in  utero  was  fed  by  the  amniotic  liquid  or  the  blood, 
and  they  also  beheved,  in  contradistinction  to  the  Peripatetics,  that 
both  male  and  female  supplied  seed  in  generation,  as  is  shown  by 
the  lines  of  Lucretius : 

usque  adeo  magni  refert,  ut  semina  possint 
seminibus  commisceri  genitaliter  apta 
crassaque  conveniant  liquidis  at  liquida  crasso. 

But  much  more  important  than  the  teaching  of  these  philosophers 
was  the  rise  of  what  might  be  called  the  scientific  faculty  of  the  great 


University  of  Alexandria.  That  seat  of  learning,  perhaps  the  most 
glorious,  after  Athens,  of  any  in  antiquity,  and  greater  than  its  con- 
temporary rival  Pergamos,  was  important  because  all  the  traditions 
of  earlier  times  were  united  in  it  like  a  bundle  of  strands  coming 
together  to  form  a  rope.  Democritean  atomism.  Peripatetic  science 
and  metaphysics,  Goan  biology,  Coan  and  Cnidian  medicine,  above 
all,  Athenian  mathematics  and  astronomy,  all  were  gathered  in 
the  fMovaelov  of  Alexandria  under  the  benevolent  dynasty  of  the 
Ptolemies.  The  link  between  the  Alexandrian  biologists  and  the 
school  of  Aristotle  was  Straton  of  Lampsacus,  who,  though  apparently 
not  making  any  contribution  to  embryology  himself,  must  have 
brought  the  knowledge  of  generation  gained  by  Aristotle  to  Alex- 
andria as  he  sailed  south  across  the  Mediterranean  to  be  the  tutor 
of  Ptolemy  Philadelphus.  The  link  between  Cos  and  Alexandria  was 
Diodes  of  Carystus,  who  was  the  last  of  the  Hippocratic  school  and 
also  a  pupil  of  Philistion  of  Locri.  Diodes  has  a  certain  importance 
in  the  history  of  embryology;  for  Oribasius  refers  to  him  as  the  dis- 
coverer of  the  punctum  saliens  in  the  mammalian  embryo,  "on  the 
ninth  day  a  few  points  of  blood,  on  the  eighteenth  beating  of  the 
heart,  on  the  twenty-seventh  traces  of  the  spinal  cord  and  head  ".  He 
thus  showed  that  the  early  development  of  chick  and  mammal  was 
very  alike.  Plutarch  also  tells  us  that  he  occupied  himself  with  the 
question  of  sterility.  He  described  the  human  placenta,  as  well  as 
embryos  of  twenty-seven  and  forty  days,  and  he  held  that  both  male 
and  female  contribute  seed  in  generation.  Cnidian  medicine  in- 
fluenced Alexandria  through  Chrysippus  of  Cnidus — not  the  Stoic — 
whose  embryological  doctrine  seems  to  have  been  that  the  embryo  had 
only  a  vegetative  soul  until  birth  or  hatching. 

All  these  influences  were  fruitful,  for  they  produced  the  two 
greatest  physiologists  of  ancient  times,  Herophilus  of  Chalcedon  and 
Erasistratus  of  Chios.  These  two,  who  were  contemporaries  during 
the  third  century  B.C.,  experimented  much  and  wrote  voluminously, 
but  all  except  fragments  of  their  writings  have  been  lost,  and  can 
now  only  be  pieced  together  out  of  the  books  of  Galen,  as  has  been 
done  by  Dobson.  Allbutt  has  well  described  the  differences  between 
them,  such  as  the  predilection  of  Herophilus  for  the  humoral  patho- 
logy and  pharmacy,  and  the  greater  interest  taken  by  Erasistratus  in 
atomistic  speculations.  "Herophilus",  says  Plutarch,  "leaveth  to 
unbome  babes  a  mooving  naturall,  but  not  a  respiration,  of  which 


Co[N-re-MPoR.A(e.r  EveNfrs  and 


motion  the  sinewes  be  the  instrumental!  cause,  but  afterwards  they 
become  perfect  Hving  animall  creatures,  when  being  come  forth  of 
the  wombe,  they  take  in  breath  from  the  aire." 

Herophilus  described  the  ovaries  and  the  Fallopian  tubes,  but  did 
not  advance  further  than  Aristotle  towards  correct  sexual  physiology 
in  this  respect.  We  gather  that  he  made  many  dissections  of  embryos 
from  the  testimony  of  Tertullian,  though  this  may  not  be  worth  much. 
Moreover,  he  called  the  outer  membrane  of  the  brain,  chorion,  after 
the  membranes  which  surround  the  embryo.  He  gave  a  correct  de- 
scription of  the  umbilical  cord,  except  that  he  assigned  to  it  four  vessels 
instead  of  three,  carrying  blood  and  breath  to  the  embryo.  The 
veins,  he  thought,  communicated  with  the  venae  cavae,  and  the 
arteries  with  the  great  artery  running  along  the  spine.  Herophilus 
also  occupied  himself  much  with  obstetrical  matters,  and  wrote  a 
treatise  on  them,  fiaicoTtKov.  Together  with  Erasistratus  he  denied 
that  there  were  any  diseases  special  to  women  other  than  those 
attendant  on  their  special  sexual  functions,  but  the  greatest  contribu- 
tion which  he  made  to  biology  was  the  association  of  the  brain  with 
the  intellect^,  for  even  Aristotle  had  made  the  he^rt  the  seat  of  the 
mental  individual. 

Erasistratus  did  not  study  embryology  as  much  as  did  Herophilus, 
but  a  passage  in  Galen  throws  an  interesting  light  on  his  notions  of 
embryonic  growth.  "The  heart",  says  Galen,  "is  no  larger  at  first 
than  a  millet  seed,  or,  if  you  like,  a  bean.  Ask  yourself  how  it  could 
grow  large  otherwise  than  by  being  distended  and  receiving  nutri- 
ment throughout  its  whole  extent,  just  as  we  have  shown  above  that 
the  seed  is  nourished.  But  even  this  is  unknown  to  Erasistratus,  who 
makes  so  much  of  Nature's  Art.  He  supposes  that  animals  grow  just 
like  a  sieve,  a  rope,  a  bag,  or  a  basket,  each  of  which  grows  by  the 
addition  to  it  of  materials  similar  to  those  out  of  which  it  began  to 
be  made."  This  is  only  one  instance  out  of  many  in  which  Galen,  the 
teleologist,  finds  fault  with  Erasistratus,  the  mechanistic  philosopher. 

During  the  period  when  the  biological  school  of  Alexandria  was 
at  its  height,  that  city  became  an  important  Jewish  centre.  Two 
centuries  later  it  was  to  produce  Philo,  but  now  the  Alexandrian 
Jews  were  writing  that  part  of  the  modern  Bible  known  as  the  Wisdom 
Literature.  In  books  such  as  the  Wisdom  of  Solomon,  Ecclesiasticus, 
Proverbs,  etc.,  the  typical  Hellenic  exclusion  of  the  action  of  gods 

^  This  was  not  absolutely  new:  Alcmaeon  had  held  the  same  view  (see  Burnet). 


in  natural  phenomena  is  clearly  to  be  seen.  There  are  two  passages 
of  embryological  importance.  Firstly,  in  the  book  of  Job  (x,  9-1 1), 
Job  is  made  to  say,  "Remember,  I  beseech  thee,  that  thou  hast 
fashioned  me  as  clay;  and  wilt  thou  bring  me  into  dust  again? 
Hast  thou  not  poured  me  out  as  milk,  and  curdled  me  like  cheese? 
Thou  hast  clothed  me  with  skin  and  flesh,  and  knit  me  together  with 
bones  and  sinews".  This  comparison  of  embryogeny  with  the  making 
of  cheese  is  interesting  in  view  of  the  fact  that  precisely  the  same 
comparison  occurs  in  Aristotle's  book  On  the  Generation  of  Animals,  as 
we  have  already  seen.  Still  more  extraordinary,  the  only  other 
embryological  reference  in  the  Wisdom  Literature,  which  occurs  in 
the  Wisdom  of  Solomon  (vii,  2),  also  copies  an  Aristotelian  theory, 
namely,  that  the  embryo  is  formed  from  (menstrual)  blood.  There 
the  speaker  says,  "In  the  womb  of  a  mother  was  I  moulded  into 
flesh  in  the  time  of  ten  months,  being  compacted  in  blood  of  the 
seed  of  man  and  the  pleasure  that  came  with  sleep".  Perhaps 
it  is  no  coincidence  that  both  these  citations  can  be  referred  back 
to  Aristotle,  and,  in  the  second  case,  even  to  Hippocrates;  perhaps 
the  Alexandrian  Jews  of  the  third  century  B.C.  were  studying  Aristotle 
as  attentively  as  Philo  Judaeus  studied  Plato  a  couple  of  hundred 
years  later. 

The  Alexandrian  school  was  directly  responsible  for  the  introduc- 
tion of  Greek  medicine  and  biology  into  Rome,  through  the  physician 
Cleophantus,  who  seems  to  have  been  particularly  interested  in 
gynaecology.  At  the  end  of  the  second  century  B.C.  and  the  beginning 
of  the  first,  Rome  received  the  first  and  greatest  of  her  Greek 
physicians,  Asclepiades  of  Parion,  who  brought  atomism  with  him. 
He  was  thus  the  Hnk  between  Epicurus  and  the  methodistic  school 
of  physicians,  and  may  have  been  a  potent  influence  upon  Lucretius. 
Again,  Alexander  Philalethes  provides  the  link  between  Cleophantus 
and  Soranus.  Soranus  lived  in  Rome  from  about  a.d.  30  tifl  just 
after  the  end  of  the  first  century,  and  so  twenty  years  before  the 
birth  of  Galen. 

Of  aU  the  ancient  writers  on  embryology,  Soranus  is  the  one  whose 
works  were  in  later  times  most  widely  appropriated,  mutilated, 
furbished  up,  quoted  from  rightly  and  wrongly,  and  generally  upset. 
Allbutt,  Barbour  and  Singer  give  accounts  of  the  way  in  which  this 
process  went  on,  and  the  whole  question  has  given  rise  to  a  con- 
siderable literature.     (See  Lachs,  Ilberg,    Sudhov,  etc.)     It   lasted 


right  into  the  Middle  Ages,  and  was  particularly  vehement  in  the 
case  of  the  treatise  on  gynaecology,  Trepl  ywaiKeLwv  Tradotv.  This  was 
translated  into  Latin  under  the  name  of  Moschion,  then  back  into 
Greek  and  finally  back  into  Latin  again.  It  is  largely  obstetrical, 
but  it  shows  an  advanced  knowledge  of  embryology,  and  especially 
an  accurate  idea  of  the  anatomy  of  the  uterus.    (See  Plate  II.) 

The  other  writers  of  this  period  are  unimportant  embryologically. 
Among  the  Greeks,  Aelian  wrote  a  De  natura  animalium,  in  which 
he  spoke  of  eggs,  but  without  adding  anything  to  our  knowledge  of 
them;  Nicander  in  his  Theriaca  refers  to  mammalian  embryos,  and 
alleges  that  they  breathe  and  eat  through  the  umbilical  cord;  and 
Oppian  has  a  few  unsystematic  remarks  about  the  embryos  of  various 
animals.  Junius  Columella's  work  on  husbandry  contains  two  chapters 
on  eggs,  but  he  was  not  much  interested  in  the  theoretical  aspect  of 
development.  In  Aulus  Gellius  we  have  the  cheese  analogy  appearing 
in  conjunction  with  obscurantist  views  about  the  powers  of  the  number 
seven.  It  is  not  generally  known  that  a  clear  statement  of  the  pre- 
formationist  or  "  Entfaltung  "  theory  of  embryogeny  occurs  in  Seneca's 
Quaestiones  naturales,  where  there  is  the  following  passage:  "In  the 
seed  are  enclosed  all  the  parts  of  the  body  of  the  man  that  shall  be 
formed.  The  infant  that  is  borne  in  his  mother's  wombe  hath  the 
rootes  of  the  beard  and  hair  that  he  shall  weare  one  day.  In  this 
little  masse  likewise  are  all  the  lineaments  of  the  bodie  and  all  that 
which  Posterity  shall  discover  in  him".  Perhaps  this  notion  was 
derived  by  Seneca  from  the  Homoeomereity  of  Anaxagoras,  for  a 
discussion  of  which  in  relation  to  embryology,  see  Cornford.  "Hair 
cannot  come  out  of  not-hair,  nor  flesh  out  of  not-flesh",  said 

The  Natural  History  of  Pliny,  that  "voluminous,  industrious,  un- 
philosophical,  gullible,  unsystematic  old  gossip",  as  Singer  justly 
calls  him,  contains  little  of  embryological  importance,  although  he 
devotes  many  sections  to  eggs,  and  what  there  is  comes  straight  from 
the  fountain-head,  Aristotle.  As,  for  example,  "All  egs  have  within 
them  in  the  mids  of  the  yolk,  a  certain  drop,  as  it  were  of  bloud, 
which  some  thinke  to  be  the  heart  of  the  chicken,  imagining  that, 
to  be  the  first  that  in  everie  bodie  is  formed  and  made ;  and  certainlie 
a  man  shall  see  it  within  the  verie  cggc  to  pant  and  leape.  As  for 
the  chick,  it  taketh  the  corporall  substance,  and  the  bodie  of  it  is 
made  of  the  white  waterish  liquor  in  the  egge,  the  yellow  yolke 


'■jj.V^ki^-vfc .  i^imj^oi^^ 

!^  Lfe<?  l^i  n   1^  tm 

J. J  O  €  ^4 

^    t    ;::   0   t  o^^fi  " 




serves  for  nourishment;  whiles  the  chick  is  unhatched  and  within  the 
egge,  the  head  is  bigger  than  all  the  bodie  besides;  and  the  eies 
that  be  compact  and  thrust  together  be  more  than  the  verie  head. 
As  the  chick  within  growes  bigger,  the  white  turneth  into  the  middest, 
and  is  enclosed  within  the  yolke.  By  the  20  day  (if  the  eggs  be  stirred) 
ye  shall  heare  the  chick  to  peepe  within  the  verie  shell;  from  that 
time  forward  it  beginneth  to  plume  and  gather  feathers ;  and  in  this 
manner  it  lies  within  the  shell,  the  head  resting  on  the  right  foot, 
and  the  same  head  under  the  right  wing,  and  so  the  yolke  by  little 
and  little  decreaseth  and  faileth".  But  the  best  way  to  illustrate 
Pliny's  embryology  is  to  copy  out  some  of  his  index,  as  follows : 

The  Table  to  the  first  Tome  of  Plinies  Naturall  Historie. 

Egs  diverse  in  colour  298 

Egs  of  birds  of  2  colours  within  the  shell  ibid. 

Egs  of  fishes  of  i  colour  ibid. 

Egs  of  birds,  serpents,  and  fishes,  how  they  differ  ibid. 

Egs  best  for  an  hen  to  sit  upon  299 

Egs  hatched  without  a  bird,  onely  by  a  kind  heat  ibid. 

Egs  how  they  be  marred  under  an  hen  ibid, 

wind-egs,  called  Hypenemia  300 

how  they  be  engendred  301 

wind-egs,  Zephyria  ibid. 

Egs  drawne  through  a  ring  ibid. 

Egs  how  they  be  best  kept  ibid. 

The  Table  to  the  second  Tome  of  Plinies  Naturall  Historie, 

Egs  of  hens  and  their  medicinable  properties  351 

yolke  of  hens  egs,  in  what  cases  it  is  medicinable  352 

Egs  all  yolke,  and  without  white,  be  called  Schista  ibid, 

skinne  of  an  Hens  egge-shell,  good  in  Physicke  ibid. 

Hens  Eggeshell  reduced  unto  ashes,  for  what  it  serveth  ibid, 

the  wonderfull  nature  of  Hens  Eggeshels  ibid. 

Hens  Egges,  all  whole  as  they  be,  what  they  are  good  for  353 

the  commendations  of  Hens  Egges,  as  a  meat  most  medicinable  ibid. 
Hens  Egge,  a  proper  nourishment  for  sicke  folks,  and  may  go 

for  meat  and  drinke  both  ibid. 

Egge-shels,  how  they  may  be  made  tender  and  pliable  ibid, 

white  of  an  Egge  resisteth  fire  ibid, 

of  Geese  Egges  a  discourse  354 
the  serpents  egge,  which  the  Latines  call  Anguinum,  what  it 

is,  and  how  engendred  355 

This  last  item  exhibits  Pliny  at  his  worst.  It  is  worth  quoting,  apart 
from  its  intrinsic  value,  for  it  shows  to  what  depths  embryological 
knowledge  descended  within  four  hundred  years  after  Aristotle  col- 
lected his  specimens  on  the  shores  of  the  lagoon  of  Pyrrha,  and  talked 
with  the  fishermen  of  Mitylene.  "I  will  not  overpasse  one  kind  of 
eggs  besides,  which  is  in  great  name  and  request  in  France,  and 
whereof  the  Greeke  authors  have  not  written  a  word ;  and  this  is 



the  serpents  egg,  which  the  Latins  call  Anguinum.  For  in  Summer 
time  yerely,  you  shall  see  an  infinit  number  of  snakes  gather  round 
together  into  an  heape,  entangled  and  enwrapped  one  within  another 
so  artificially,  as  I  am  not  able  to  expresse  the  manner  thereof;  by 
the  means  therefore,  of  the  froth  or  salivation  which  they  yeeld  from 
their  mouths,  and  the  humour  that  commeth  from  their  bodies, 
there  is  engendred  the  egg  aforesaid.  The  priests  of  France,  called 
Druidae^,  are  of  opinion,  and  so  they  deliver  it,  that  these  serpents 
when  they  have  thus  engendred  this  egg  do  cast  it  up  on  high  into 
the  aire  by  the  force  of  their  hissing,  which  being  observed,  there 
must  be  one  ready  to  catch  and  receive  it  in  the  fall  again  (before 
it  touch  the  ground)  within  the  lappet  of  a  coat  of  arms  or  souldiours 
cassocks.  They  affirme  also  that  the  party  who  carrieth  this  egg  away, 
had  need  to  be  wel  mounted  upon  a  good  horse  and  to  ride  away 
upon  the  spur,  for  that  the  foresaid  serpents  will  pursue  him  still, 
and  never  give  over  until  they  meet  with  some  great  river  betweene 
him  and  them,  that  may  cut  off  and  intercept  their  chace.  They  ad 
moreover  and  say  that  the  only  marke  to  know  this  egg  whether  it 
be  right  or  no,  is  this,  that  it  will  swim  aloft  above  the  water  even 
against  the  stream,  yea  though  it  were  bound  and  enchased  with  a 
plate  of  gold."  But  one  must  not  be  too  severe  upon  Pliny,  for  he 
and  his  translator,  Philemon  Holland,  provide  an  entertainment 
unequalled  anywhere  else. 

To  some  extent  the  same  applies  to  Plutarch  of  Chaeronea,  who 
lived  about  the  same  time.  Plutarch's  writings,  inspired  as  they  were 
throughout  by  the  desire  to  commend  the  ancient  religion  of  Greece 
to  a  degenerate  age,  represent  no  milestone  or  turning-point  in  the 
history  of  embryology,  yet  there  is  a  passage  in  the  Symposiaques,  or 
Table-questions  which  bears  upon  it.  The  third  question  of  book  2 
is  "Whether  was  before,  the  hen  or  egg?"  "This  long  time",  says 
Plutarch,  "I  absteined  from  eating  egges,  by  reason  of  a  certaine 
dream  I  had,  and  the  companie  conceived  an  opinion  or  suspition 
of  me  that  there  were  entred  into  my  head  the  fantasies  and  super- 
stitions of  Orpheus  or  Pythagoras,  and  that  I  abhorred  to  eat  an 
egge  for  that  I  believed  it  to  be  the  principle  and  fountaine  of  genera- 
tion." He  then  makes  the  various  characters  in  the  dialogue  speak 
to  the  motion,  and  one  of  them,  Firmus,  ends  his  speech  thus,  "And 

^  For  further  information  about  the  serpent's  eggs  of  the  Druids,  see  Kendrick;  they 
were  probably  fossil  echinoderms. 


now  for  that  which  remaineth  (quoth  he  and  therewith  he  laughed) 
I  will  sing  unto  those  that  be  skilfull  and  of  understanding  one  holy 
and  sacred  sentence  taken  out  of  the  deepe  secrets  of  Orpheus,  which 
not  onely  importeth  this  much,  that  the  cgge  was  before  the  henne, 
but  also  attributeth  and  adjudgeth  to  it  the  right  of  eldership  and 
priority  of  all  things  in  the  world,  as  for  the  rest,  let  them  remaine 
unspoken  of  in  silence  (as  Herodotus  saith)  for  that  they  bee  exceeding 
divine  and  mysticall,  this  onely  will  I  speake  by  the  way;  that  the 
world  containing  as  it  doth  so  many  sorts  and  sundry  kinds  of  living 
creatures,  there  is  not  in  manner  one,  I  dare  well  say,  exempt  from 
being  engendred  of  an  egge,  for  the  egge  bringeth  forth  birdes  and 
foules  that  fiie,  fishes  an  infinit  number  that  swimme,  land  creatures, 
as  lizards,  such  as  live  both  on  land  and  water  as  crocodiles,  those 
that  bee  two-footed,  as  the  bird,  such  as  are  footlesse,  as  the  serpent, 
and  last  of  all,  those  that  have  many  feet,  as  the  unwinged  locust. 
Not  without  great  reason  therefore  is  it  consecrated  to  the  sacred 
ceremonies  and  mysteries  of  Bacchus  as  representing  that  nature 
which  produceth  and  comprehendeth  in  itselfe  all  things".  This 
emphatic  passage  looks  at  first  sight  as  if  it  was  a  statement  of 
the  Harveian  doctrine  omne  vivum  ex  ovo.  But  the  fact  that  no 
mammals  are  mentioned  makes  this  improbable.  Firmus  then  sits 
down  and  Senecius  opposes  him  with  the  well-worn  argument  that 
the  perfect  must  precede  the  imperfect,  laying  stress  also  on  the 
occurrence  of  spontaneous,  i.e.  eggless,  generation,  and  on  the  fact 
that  men  could  find  no  "row"  in  eels.  Three  hundred  years  later, 
Ambrosius  Macrobius  handled  the  question  again  (see  Whittaker), 
and  the  progress  in  embryological  knowledge  could  be  strikingly 
shown  by  the  difference  in  treatment.  It  would  be  an  interesting 
study  to  make  a  detailed  comparison  of  them. 

1-6.    Galen 

Another  fifty  years  brings  us  to  Galen  of  Pergamos,  second  in 
greatness  among  ancient  biologists,  though  in  spite  of  his  multi- 
tudinous writings  he  does  not  quite  take  this  high  rank  in  embiyology. 
That  knowledge  of  the  development  of  the  foetus  was  at  this  time 
specially  associated  with  Peripatetic  tradition  appears  from  a  remark 
of  Lucian  of  Samosata,  Galen's  contemporary.  In  the  satire  called, 
The  Auction  of  the  Philosophies,  Hermes,  the  auctioneer,  referring  to  the 
Peripatetic  who  is  being  sold,  says,  "He  will  tell  you  all  about  the 


shaping  of  the  embryo  in  the  womb".  But  Galen  was  now  to  weld 
together  all  the  biological  knowledge  of  antiquity  into  his  voluminous 
works,  and  so  transmit  it  to  the  Middle  Ages. 

Most  of  Galen's  writing  was  done  between  a.d.  150  and  180.  Out 
of  the  twenty  volumes  of  Kiihn's  edition  of  1829,  l^^s  than  one  is 
concerned  with  embryology,  a  proportion  considerably  less  than  in 
the  case  of  Aristotle.  Galen's  embryology  is  to  be  found  in  his 
Trepl  (f)V(nKcov  Svvdfiecov,  On  the  Natural  Faculties,  which  contains  the 
theoretical  part,  and  in  his  On  the  Formation  of  the  Foetus,  which  con- 
tains the  more  anatomical  part.  There  is  also  the  probably  spurious 
treatise  et  ^mov  to  Kara  <yaa-Tp6<i,  On  the  Question  of  whether  the  Embryo 
is  an  Animal. 

It  is  important  to  realise  at  the  outset  that  Galen  was  a  vitalist 
and  a  teleologist  of  the  extremest  kind.  He  regarded  the  living  being 
as  owing  all  its  characteristics  to  an  indwelling  Physis  or  natural 
entity  with  whose  "faculties"  or  powers  it  was  the  province  of 
physiology  to  deal.  The  living  organism  according  to  him  has  a  kind 
of  artistic  creative  power,  a  t6xvv>  which  acts  on  the  things  around 
it  by  means  of  the  faculties,  Swd/xei's,  by  the  aid  of  which  each  part 
attracts  to  itself  what  is  useful  and  good  for  it,  rb  oUelov,  and 
repels  what  is  not,  to  aXXorptov.  These  faculties,  such  as  the  "peptic 
faculty"  in  the  stomach  and  the  "sphygmic  faculty"  in  the  heart, 
are  regarded  by  Galen  as  the  causes  of  the  specific  functions  or 
activity  of  the  part  in  question.  They  are  ultimate  biological  cate- 
gories, for,  although  he  admits  the  theoretical  possibility  of  analysing 
them  into  simpler  components,  he  never  makes  any  attempt  to  do 
so,  and  evidently  regards  such  an  effort  as  doomed  to  failure,  unlike 
Roux,  whose  "interim  biological  laws"  are  really  conceived  of  as 
interim.  "The  effects  of  Nature",  says  Galen,  "while  the  animal  is 
still  being  formed  in  the  womb  are  all  the  different  parts  of  the  body, 
and  after  it  has  been  born  an  effect  in  which  all  parts  share  is  the 
progress  of  each  to  its  full  size  and  thereafter  the  maintenance  of 
itself  as  long  as  possible."  Galen  divides  the  effects  of  the  faculties 
into  three.  Genesis,  Growth,  and  Nutrition,  and  means  by  the  first 
what  we  mean  by  embryogeny.  "Genesis",  he  says,  "is  not  a  simple 
activity  of  Nature,  but  is  compounded  of  alteration  and  of  shaping. 
That  is  to  say,  in  order  that  bone,  nerve,  veins,  and  all  other  tissues 
may  come  into  existence,  the  underlying  substance  from  which  the 
animal  springs  must  be  altered;  and  in  order  that  the  substance  so 


altered  may  acquire  its  appropriate  shape  and  position,  its  cavities, 
outgrowths,  and  attachments,  and  so  forth,  it  has  to  undergo  a 
shaping  or  formative  process.  One  would  be  justified  in  calling  this 
substance  which  undergoes  alteration  the  material  of  an  animal,  just 
as  wood  is  the  material  of  a  ship  and  wax  of  an  image."  In  this 
remarkable  passage,  Galen  expresses  modern  views  about  chemical 
growth  and  chemical  differentiation. 

Galen  then  goes  on  to  treat  of  embryogeny  in  more  detail.  "The 
seed  having  been  cast  into  the  womb  or  into  the  earth — for  there  is 
no  difference — ",  he  says  (see  p.  65),  "then  after  a  certain  definite 
period  a  great  number  of  parts  become  constituted  in  the  substance 
which  is  being  generated;  these  differ  as  regards  moisture,  dryness, 
coldness  and  warmth,  and  in  all  the  other  qualities  which  naturally 
derive  therefrom",  such  as  hardness,  softness,  viscosity,  friability, 
lightness,  heaviness,  density,  rarity,  smoothness,  roughness,  thickness, 
and  thinness.  "Now  Nature  constructs  bone,  cartilage,  nerve,  mem- 
brane, ligament,  vein,  and  so  forth  at  the  first  stage  of  the  animal's 
genesis,  employing  at  this  task  a  faculty  which  is,  in  general  terms, 
generative  and  alterative,  and,  in  more  detail,  warming,  chilHng, 
drying  and  moistening,  or  such  as  spring  from  the  blending  of  these, 
for  example,  the  bone-producing,  nerve-producing,  and  cartilage- 
producing,  faculties  (since  for  the  sake  of  clearness  these  terms  must  be 
used  as  well) ....  Now  the  peculiar  flesh  of  the  liver  is  of  a  certain  kind 
as  well,  also  that  of  the  spleen,  that  of  the  kidneys  and  that  of  the 
lungs,  and  that  of  the  heart,  so  also  the  proper  substance  of  the  brain, 
stomach,  oesophagus,  intestines  and  uterus  is  a  sensible  element,  of 
similar  parts  all  through,  simple  and  uncompounded. .  . .  Thus  the 
special  alterative  faculties  in  each  animal  are  of  the  same  number 
as  the  elementary  parts,  and  further,  the  activities  must  necessarily 
correspond  each  to  one  of  the  special  parts,  just  as  each  part  has  its 
special  use. .  .  .  As  for  the  actual  substance  of  the  coats  of  the  stomach, 
intestine,  and  uterus,  each  of  these  has  been  rendered  what  it  is  by 
a  special  alterative  faculty  of  nature;  while  the  bringing  of  these 
together,  the  combination  therewith  of  the  structures  that  are  in- 
serted into  them,  etc.  have  all  been  determined  by  a  faculty  which 
we  call  the  shaping  or  formative  faculty;  this  faculty  we  also  state 
to  be  artistic — nay,  the  best  and  highest  art — doing  everything  for 
some  purpose,  so  that  there  is  nothing  ineffective  or  superfluous,  or 
capable  of  being  better  disposed." 


Thus  the  alterative  faculty  takes  the  primitive  unformed  raw 
material  and  changes  it  into  the  different  forms  represented  by  the 
different  tissues,  while  the  formative  faculty,  acting  teleologically 
from  within,  organises  these  building-stones,  as  it  were,  into  the 
various  temples  which  make  up  the  Acropolis  of  the  completed 
animal.  Galen  next  goes  on  to  speak  of  the  faculty  of  growth.  "Let 
us  first  mention",  he  says,  "that  this  too  is  present  in  the  foetus 
in  utero  as  is  also  the  nutritive  faculty,  but  that  at  that  stage  these 
two  faculties  are,  as  it  were,  handmaids  to  those  already  mentioned, 
and  do  not  possess  in  themselves  supreme  authority." 

Later  on,  until  full  stature  is  reached,  growth  is  predominant,  and 
finally  nutrition  assumes  the  hegemony. 

So  much  for  Galen's  embryological  theory.  But  before  leaving  the 
treatise  On  the  Natural  Faculties,  it  may  be  noted  that  he  ascribes  a 
retentive  faculty  to  the  uterus  as  well  as  to  the  stomach,  and  explains 
birth  as  being  due  to  a  cessation  of  action  on  the  part  of  the  retentive 
faculty,  "when  the  object  of  the  uterus  has  been  fulfilled",  and  a 
coming  into  action  of  a  hitherto  quiescent  propulsive  faculty.  This 
wholesale  allotting  of  faculties  can  obviously  be  made  to  explain 
anything,  and  is  eminently  suited  to  a  teleological  account  such  as 
Galen's.  It  was  not  inconvenient  as  a  framework  within  which  all 
the  biological  knowledge  of  antiquity  could  be  crystallised,  but  it  was 
utterly  pernicious  to  experimental  science.  Fifteen  hundred  years  later 
it  received  what  would  have  been  the  death-blow  to  any  less  virile 
theory,  at  the  hands  of  Moliere  in  his  immortal  Malade  Imaginaire : 

Bachelirius.    Mihi  a  docto  doctore 

Demandatur  causam  et  rationem  quare 
Opium  facit  dormire 
A  quoi  respondeo 
Quia  est  in  eo 
Virtus  dormitiva 
Cujus  est  nature 
Sensus  assoupire. 
Chorus.    Bene,  bene,  bene,  bene  respondere. 
Dignus,  dignus  est  entrare 
In  nostro  docto  corpore. 
Bene,  bene,  respondere. 

But  to  return  to  Galen.  The  book  on  the  formation  of  the  embryo 
opens  with  a  historical  account  of  the  views  of  the  Hippocratic  writers 


with  whom  Galen  was  largely  in  agreement.  It  goes  on  to  describe 
the  anatomy  of  allantois,  amnios,  placenta,  and  membranes  with 
considerable  accuracy.  The  embryonic  life  consists,  it  says,  of  four 
stages:  (i)  an  unformed  seminal  stage,  (2)  a  stage  in  which  the  tria 
principia  (a  concept  here  met  with  for  the  first  time)  are  engendered, 
the  heart,  liver  and  brain,  (3)  a  stage  when  all  the  other  parts  are 
mapped  out  and  (4)  a  stage  when  all  the  other  parts  have  become 
clearly  visible.  Parallel  with  this  development,  the  embryo  also  rises 
from  possessing  the  life  of  a  plant  to  that  of  an  animal,  and  the 
umbilicus  is  made  the  root  in  the  analogy  with  a  plant.  The  embryo 
is  formed,  firstly,  from  menstrual  blood,  and  secondly,  from  blood 
brought  by  the  umbilical  cord,  and  the  way  in  which  it  turns  into 
the  embryo  is  made  clearer  as  follows:  "If  you  cut  open  the  vein 
of  an  animal  and  let  the  blood  flow  out  into  moderately  hot  water; 
the  formation  of  a  coagulum  very  like  the  substance  of  the  liver  will 
be  seen  to  take  place".  And  in  effect  this  viscus,  according  to  Galen, 
is  formed  before  the  heart. 

Galen  also  taught  that  the  embryo  excreted  its  urine  into  the 
allantois,  and  was  acquainted  with  foetal  atrophy.  He  gave  a  fairly 
correct  account  of  the  junction  of  the  umbilical  veins  with  the 
branches  of  the  portal  vein,  and  the  umbilical  with  the  iliac  arteries, 
of  the  foramen  ovale,  the  ductus  Arantii  and  the  ductus  Botalli.  He 
maintained  that  the  embryo  respired  through  the  umbilical  cord, 
and  said  that  the  blood  passed  in  the  embryo  from  the  heart  to  the 
lungs  and  not  vice  versa.  The  belief  that  male  foetuses  were  formed 
quicker  than  female  ones  he  still  entertained,  and  explained  as  being 
due  to  the  superior  heat  and  dryness  of  the  male  germ.  He  also 
associated  the  male  conception  with  the  right  side  and  the  female 
with  the  left  and  asserted  that  the  intra-uterine  movements  are  sooner 
felt  in  the  case  of  the  male  than  in  the  case  of  the  female.  Dry  foods 
eaten  by  the  mother,  he  thought,  would  lead  to  a  more  rapid  develop- 
ment of  the  foetus  than  other  kinds. 

In  this  account  of  the  Galenic  embryology  I  have  drawn  not  only 
upon  the  book  on  the  formation  of  the  foetus,  but  also  upon  his 
v7r6fMV7]/jba,  Commentary  on  Hippocrates,  his  Trepl  alricov  av/jLTTTco/naTcov, 
On  the  Causes  of  Symptoms,  and  his  book  Trepl  %peta?  tmv  fjuoplcor,  On  the 
Use  of  Parts.  It  is  this  latter  work  that  had  the  greatest  influence  on  the 
ages  which  followed  Galen's  Hfe.  In  the  course  of  seventeen  books,  he 
tries  to  demonstrate  the  value  and  teleological  significance  of  every 


structure  and  function  in  the  human  and  animal  body,  and  to  show 
that,  being  perfectly  adapted  to  its  end,  it  could  not  possibly  be  other  in 
shape  or  nature  than  what  it  is.  At  the  conclusion  of  this  massive  work 
with  all  its  extraordinary  ingenuity  and  labour,  he  says,  "Such  then 
and  so  great  being  the  value  of  the  argument  now  completed,  this 
section  makes  it  all  plain  and  clear  like  a  good  epode — I  say  an  epode, 
but  not  in  the  sense  of  one  who  uses  enchantments  (eVwSat?)  but  as 
in  the  melic  poets  whom  some  call  lyric,  there  is  as  well  as  strophe 
and  antistrophe,  an  epode,  which,  so  it  is  said,  they  used  to  sing 
standing  before  the  altar  as  a  hymn  to  the  Gods.  To  this  then  I 
compare  this  final  section  and  therefore  I  have  called  it  by  that 
name".  This  is  one  of  the  half-dozen  most  striking  paragraphs  in 
the  history  of  biology ;  worthy  to  rank  with  the  remarks  of  Hippo- 
crates on  the  "  Sacred  Disease".  Galen,  as  he  wrote  the  words,  must 
have  thought  of  the  altar  of  Dionysus  in  the  Athenian  or  Pergamene 
theatre,  made  of  marble  and  hung  about  with  a  garland,  but  they 
were  equally  applicable  to  the  altar  of  a  basilica  of  the  Christian 
Church  with  the  bishop  and  his  priests  celebrating  the  liturgy  at  it. 
What  could  be  more  charged  with  significance  than  this?  At  the 
end  of  the  antique  epoch  the  biology  of  all  the  schools,  Croton, 
Akragas,  Cos,  Cnidus,  Athens,  Alexandria,  Rome,  is  welded  together 
and  as  it  were  deposited  at  the  entrance  into  the  sanctuary  of 
Christendom.  It  was  the  turning-point,  in  Spengler's  terminology, 
between  ApoUinian  civilisation  and  Faustian  culture.  Galen's  words 
are  the  more  extraordinary,  for  he  himself  can  hardly  have  foreseen 
that  the  long  line  of  experimentalists  which  had  arisen  in  the  sixth 
century  B.C.  would  come  to  an  end  with  him.  But  so  it  was  to  be, 
and  thenceforward  experimental  research  and  biological  speculation 
were  alike  to  cease,  except  for  a  few  stray  mutations,  born  out  of 
due  time,  until  in  1453  the  city  of  Byzantium  should  burst  like  .a 
ripe  pod  and,  distributing  her  scholars  all  over  the  West,  as  if  by 
a  fertilising  process,  bring  all  the  fruits  of  the  Renaissance  into  being. 



2-1.    Patristic,  Talmudic,  and  Arabian  Writers 

We  are  now  at  the  beginning  of  the  second  century  a.d.  The  next 
thousand  years  can  be  passed  over  in  as  short  a  time  as  it  has  taken 
to  describe  the  embryology  of  Galen  alone.  The  Patristic  writers, 
who  on  the  whole  were  careful  to  base  their  psychology  on  the 
physiology  of  the  ancients,  had  little  to  say  about  the  developing 
embryo.  Most  of  their  interest  in  it  was,  as  would  naturally  be 
expected,  theological;  Tertullian,  for  instance,  held  that  the  soul  was 
present  fully  in  the  embryo  throughout  its  intra-uterine  life,  thus 
denying  that  kind  of  psychological  recapitulation  which  had  been 
suggested  by  Aristotle.  "Reply,"  he  says  in  his  De  Anima,  "O  ye 
Mothers,  and  say  whether  you  do  not  feel  the  movements  of  the 
child  within  you.  How  then  can  it  have  no  soul?  "  These  views  were 
not  held  by  other  Fathers,  of  whom  St  Augustine  of  Hippo  {De 
Immortalitate  et  de  quantitate  ahimae)  may  serve  as  a  representative,  for 
he  thought  that  the  embryo  was  "besouled"  in  the  second  month 
and  "besexed"  in  the  fourth.  These  various  opinions  were  duly 
reflected  in  the  law,  and  abortion,  which  had  even  been  recom- 
mended theoretically  by  Plato  and  defended  practically  by  Lysias 
in  the  fourth  or  fifth  century  B.C.,  now  became  equivalent  to  homicide 
and  punishable  by  death.  This  fact  leads  Singer  to  the  view  that 
the  Hippocratic  oath  is  late,  perhaps  early  Christian.  The  late  Roman 
law,  which,  according  to  Spangenberg,  regarded  the  foetus  as  not 
''Homo'",  not  even  '' Infans'\  but  only  a  ''Spes  animantis'\  was 
gradually  replaced  by  a  stern  condemnation  of  all  pre-natal  infanti- 
cide. "And  we  pay  no  attention",  said  the  Bishops  of  the  Quinisext 
Council,  held  at  Byzantium  in  692,  "to  the  subtle  distinction  as  to 
whether  the  foetus  is  formed  or  unformed."  Other  authorities,  follow- 
ing St  Augustine,  took  a  more  liberal  view,  and  the  canon  law  as  finally 
crystallised  recognised  first  the  fortieth  day  for  males  and  the  eightieth 
day  for  females  as  the  moment  of  animation,  but  later  the  fortieth 
day  for  both  sexes.    The  ''embryo  informatus"  thus  had  no  soul,  the 

92  EMBRYOLOGY   FROM   GALEN  [pt.  ii 

^'^ embryo  formatus"  had,  and  as  a  corollary  could  be  baptised. 
St  Thomas  Aquinas  was  of  opinion  that  embryos  dying  in  utero  might 
possibly  be  saved :  but  Fulgentius  denied  it.  As  for  the  ancient  belief 
that  male  embryos  were  formed  twice  as  quickly  as  female  ones,  it 
lingered  on  until  Goelicke  took  the  trouble  to  disprove  it  experi- 
mentally in  1723. 

Clement  of  Alexandria,  in  his  book  \6<yo<i  TrporpeTTriKO'i  Trpo? 
"EX\.7]va'i,  has  some  remarks  to  make  on  embryology,  but  adds  nothing 
to  the  knowledge  previously  gained.  He  adopts  the  Peripatetic  view 
that  generation  results  from  the  combination  of  semen  with  menstrual 
blood,  and  he  uses  the  Aristotelian  illustration  of  rennet  coagulating 
milk.  Lactantius  of  Nicomedia,  who  lived  about  the  date  of  the 
Nicene  Council  (a.d.  325)  perpetuated  the  deeply-rooted  association 
of  male  with  right  and  female  with  left  in  his  book  On  the  work  of 
God,  De  opificio  Dei.  He  also  maintained  that  the  head  was  formed 
before  the  heart  in  embryogeny,  and  seems  to  have  opened  hen's 
eggs  systematically  at  different  stages,  so  that  to  this  extent  he  was 
a  better  embryologist  than  Galen.  St  Gregory  of  Nyssa,  as  we  have 
already  seen  (p.  20),  evolved  a  neo-vitalistic  theory  which  he  ap- 
plied to  the  growth  of  the  embryo. 

Late  Latin  writers,  other  than  the  theologians,  do  not  say  much 
about  it.  There  is  a  passage  in  Ausonius,  however,  which  describes 
the  development  of  the  foetus  {Eclog.  de  Rat.  puerp.)  but  it  is  almost 
wholly  astrological.    Elsewhere  he  says: 

juris  idem  tribus  est,  quod  ter  tribus;  omnia  in  istis; 
forma  hominis  coepti,  plenique  exactio  partu, 
quique  novem  novies  fati  tenet  ultima  finis. 

Idyll  II  (Gryphus  ternarii  numeri),  4-6. 
(The  power  of  3,  in  3  times  3  lies  too, 
Thus  9  rules  human  form  and  human  birth, 
And  9  times  9  the  end  of  human  life.) 

But  this  is  probably  a  late  echo  of  the  Pythagoreans  rather  than 
an  early  prelude  to  Leonardo  da  Vinci  and  the  mathematisation  of 

That  great  mass  of  Jewish  writings  known  as  the  Talmud,  which 
grew  up  between  the  second  and  sixth  centuries  a.d.,  also  contains 
some  references  to  embryology,  and  certain  Jewish  physicians,  such 
as  Samuel-el-Yehudi,  of  the  second  century,  are  said  to  have  devoted 


special  attention  to  it.  The  embryo  was  called  peri  habbetten  (fruit  of 
the  body),  ]a2n  ns.    It  grew  through  various  definite  stages: 

(i)  golem  (formless,  rolled-up  thing),  nbu,  0-1-5  months. 

(2)  shefir  meruqqdm  (embroidered  foetus),  api»  T'Dit. 

(3)  ^ubbar  (something  carried),  imi?,  1-5-4  months. 

(4)  walad  (child),  n*?!,  4-7  months. 

(5)  walad shel  qaydmd  (viable  child),  so'^^p '7tri'?i,  7-9  months. 

(6)  ben  she-kallu  khaddshdw  (child  whose  months  have  been  com- 
pleted), rirnn  I'^rir  ]n. 

The  ideas  of  the  Talmudic  writers  on  the  life  led  by  the  embryo 
in  utero  are  well  represented  by  the  remark,  "It  floateth  like  a  nut- 
shell on  the  waters  and  moveth  hither  and  thither  at  every  touch" 

ms  o*»  "rtr  ':'SDn  niia  TUNb  las  •'^lan  n»n  n'?i  rrch  ity'^s  •'sn  lasi 

And  the  classical  passage,  "Rabbi  Simlai  lectured:  the  babe  in  its 
mother's  womb  is  like  a  rolled-up  scroll,  with  folded  arms  lying 
closely  pressed  together,  its  elbows  resting  on  its  hips,  its  heels  against 
its  buttocks,  its  head  between  its  knees.  Its  mouth  is  closed,  its  navel 
open.  It  eats  its  mother's  food  and  sips  its  mother's  drink:  but  it 
doth  not  excrete  for  fear  of  hurting" 

bv  rT*  niioi  "rsipa'!^  Q^ith  las  "'yan  n»n  n'^in  rxh  ''V^b's^^  •'in  tJ^m 
ittNtr  na»  nmtyi  n'?sis  las:^  n»»  '?2isi  mns  "nuai  miio  rsi  rsin  ^■'n  i"? 

It  was  thought,  moreover,  that  the  bones  and  tendons,  the  nails, 
the  marrow  in  the  head  and  the  white  of  the  eye,  were  derived  from 
the  father,  "who  sows  the  white",  but  the  skin,  flesh,  blood,  hair, 
and  the  dark  part  of  the  eye  from  the  mother,  "who  sows  the  red". 
This  is  evidently  in  direct  descent  from  Aristotle  through  Galen,  and 
may  be  compared  with  the  following  passage  from  the  latter  writer's 
Commentary  on  Hippocrates:  "We  teach  that  some  parts  of  the  body 
are  formed  from  the  semen  and  the  flesh  alone  from  blood.  But 
because  the  amount  of  semen  which  is  injected  into  the  uterus  is 
small,  growth  and  increment  must  come  for  the  most  part  from  the 
blood".  It  might  thus  appear  that,  just  as  the  Jews  of  Alexandria 
were  reading  Aristotle  in  the  third  century  B.C.,  and  incorporating 



94  EMBRYOLOGY   FROM   GALEN  [pt.  ii 

him  into  the  Wisdom  Literature,  so  those  of  the  third  century  a.d. 
were  reading  Galen  and  incorporating  him  into  the  Talmud.  As  for 
God,  he  contributed  the  life,  the  soul,  the  expression  of  the  face,  the 
functions  of  the  different  parts.  This  participation  of  three  factors  in 
generation,  male,  female,  and  god,  is  exceedingly  ancient,  as  may 
be  read  in  Robertson  Smith.  Some  Talmudic  writers  held  that 
development  began  with  the  head,  agreeing  with  Lactantius,  and 
others  that  it  began  at  the  navel,  agreeing  with  Alcmaeon.  Weber 
has  given  an  account  of  the  Talmudic  beliefs  about  the  infusion  of 
the  soul  into  the  embryo.  They  do  not  seem  to  have  embodied  any 
new  or  striking  idea. 

Although  the  Talmud  contained  certain  references  of  embryo- 
logical  interest,  the  first  Hebrew  treatise  on  biology  was  not  composed 
till  the  tenth  century,  when  Asaph  Judaeus  or  Asaph-ha-Yehudi 
wrote  on  embryology  about  a.d.  950.  His  MSS.  are  exceedingly 
rare,  but,  according  to  Gottheil's  description,  they  contain  several 
sections  on  embryology.  Steinschneider  has  given  another  descrip- 
tion of  them.  For  further  details  on  the  whole  subject  of  Jewish 
embryology  see  Macht. 

Arabian  science,  so  justly  famed  for  its  successes  in  certain  branches, 
was  not  of  great  help  to  embryology.  Abu-1-Hasan  ' Ali  ibn  Sahl  ibn 
Rabban  al-Tabari,  a  Moslem  physician  who  flourished  under  the 
Caliphate  of  al-Mutawakldl  about  a.d.  850,  wrote  a  book  called 
The  Paradise  of  Wisdom,  in  which  an  entire  part  was  devoted  to 
embryology,  all  the  more  interesting  as  it  is  a  mixture  of  Greek  and 
ancient  Indian  knowledge.  Browne  gives  a  description  of  it.  Ibn 
Rabban's  contemporary,  Thabit  ibn  Qurra,  is  also  said  to  have 
written  on  embryology.  The  great  Avicenna,  or,  to  give  him  his 
proper  name,  Abu  'Ali-1-Hasan  ibn  'Abdallah  ibn  Sina,  who  lived 
from  978  to  1036,  devoted  certain  chapters  of  his  Canon  Medicinae  to 
the  development  of  the  foetus,  but  added  nothing  to  Galen.  His 
contemporaries,  Abu-1-Qasim  Maslama  ibn  Ahmad  al-Majriti  and 
Arib  ibn  Said  al-Katib,  a  Spanish  Moslem,  wrote  treatises  on  the 
generation  of  animals,  but  neither  has  survived. 

What  was  alchemy  doing  all  this  time?  It  was  engaged  on  many 
curious  pursuits,  but  among  them  the  interpretation  of  embryonic 
development  was  not  one.  Alchemical  texts  before  the  tenth  century 
do  make  reference  to  eggs  from  time  to  time,  but  it  is  safe  to  say 
never  with  any  trace  of  an  interest  in  the  development  of  the  embryo 


out  of  them.    One  example  taken  from  Berthelot's  collection  will 
suffice;  it  comes  from  the  "6th  book  of  the  Philosopher"  (Syriac). 

To  make  water  of  eggs 

Take  as  many  eggs  as  you  wish,  break  them  and  put  the  whites  in  a 
glass  flask,  place  this  in  another  vessel  and  surround  it  with  fresh  horse- 
dung  up  to  the  neck  of  the  vessel.  Leave  it  so  for  15  days  changing  the 
dung  every  5  days.  Then  distil  the  liquid  in  an  alembic  and  taking  a 
pound  of  the  distillate  add  lime  of  eggs  2  ozs.  Shake  well  and  distil  again. 
Do  this  4  times.  Take  then  of  elixir  of  arsenic,  2  parts,  of  sulphur  i  part, 
of  pyrites  and  magnesia,  each  i  part.  Pound  in  a  mortar  and  add  to  the 
final  distillate  from  the  eggs.  Do  this  for  7  days  always  working  in  the 
sunlight,  once  at  sunrise,  once  in  the  middle  of  the  day,  and  once  at 
sunset.  When  this  has  been  done,  dry  the  mixture,  pound  it,  and  set  it 

I  could  only  find  one  reference  to  the  embryo  in  a  hen's  egg  among 
the  vast  number  of  alchemical  directions  of  this  time,  and  then  only 
as  a  constituent  of  the  egg  which  must  be  discarded.  As  we  shall  see, 
it  is  not  until  after  the  time  of  Paracelsus  that  the  notion  of  applying 
chemical  methods  to  eggs  or  embryos  arises  at  all. 

2-2.    St  Hildegard:  the  Lowest  Depth 

Not  long  after  the  death  of  Avicenna,  St  Hildegard  was  born. 
She  lived  from  1098  to  1180,  and  was  Abbess  successively  of  Disi- 
bodenberg  and  Bingen  in  the  Rhineland.  Her  treatises  on  the  world, 
which  are  an  extraordinary  medley  of  theological,  mystical,  scientific 
and  philosophical  speculation,  have  been  described  in  detail  by 
Singer,  and,  though  in  the  books.  Liber  Scivias  and  Liber  Divinorum 
Operum  simplicis  hominis,  there  is  little  of  embryological  interest,  yet 
she  does  give  an  account  of  development  and  especially  of  the  entry 
of  the  soul  into  the  foetus. 

This  is  illustrated  in  Plate  HI  taken  from  the  Wiesbaden  Codex  B 
of  the  Liber  Scivias.  The  soul  is  here  shown  passing  down  from  heaven 
into  the  body  of  the  pregnant  woman  and  so  to  the  embryo  within 
her.  The  divine  wisdom  is  represented  by  a  square  object  with  its 
angles  pointing  to  the  four  corners  of  the  earth  in  symbol  of  stabihty. 
From  it  a  long  tube-Hke  process  descends  into  the  mother's  womb 
and  down  it  the  soul  passes  as  a  bright  object,  "spherical"  or  "shape- 
less", illuminating  the  whole  body.  The  scene  shows  the  mother  in 
the  foreground  lying  down ;  inside  her  there  are  traces  of  the  foetal 
membranes;  behind  this  ten  persons  are  grouped,  each  carrying  a 

96  EMBRYOLOGY   FROM   GALEN  [pt.  ii 

vessel,  into  one  of  which  a  fiend  pours  some  noxious  substance  from 
the  left-hand  corner.  St  Hildegard  describes  and  expounds  the  scene 
as  follows:  "Behold,  I  saw  upon  earth  men  carrying  milk  in  earthen 
vessels  and  making  cheeses  therefrom.  Some  was  of  the  thick  kind 
from  which  firm  cheese  is  made,  some  of  the  thinner  sort  from  which 
more  porous  cheese  is  made,  and  some  was  mixed  with  corruption 
and  of  the  sort  from  which  bitter  cheese  is  made.  And  I  saw  the  like- 
ness of  a  woman  having  a  complete  human  form  within  her  womb. 
And  then  by  a  secret  disposition  of  the  most  high  craftsman,  a  fiery 
sphere  having  none  of  the  lineaments  of  a  human  body  possessed  the 
heart  of  the  form  and  reached  the  brain  and  transfused  itself  through 
all  the  members. .  .  .  And  I  saw  that  many  circling  eddies  possessed 
the  sphere  and  brought  it  earthward,  but  with  ever  renewed  force 
it  returned  upwards  and  wailed  aloud,  asking,  'I,  wanderer  that  I 
am,  where  am  I?'  'In  death's  shadow.'  'And  where  go  I?'  'In  the 
way  of  sinners.'  'And  what  is  my  hope? '  '  That  of  all  wanderers.' .  .  . 
As  for  those  whom  thou  hast  seen  carrying  milk  in  earthen  vessels,  they 
are  in  the  world,  men  and  women  alike,  having  in  their  bodies  the 
seed  of  mankind  from  which  are  procreated  the  various  kinds  of 
human  beings.  Part  is  thickened  because  the  seed  in  its  strength 
is  well  and  truly  concocted  and  this  produces  forceful  men  to  whom 
are  allotted  gifts  both  spiritual  and  carnal.. .  .And  some  had  cheeses 
less  firmly  curdled,  for  in  their  feebleness  they  have  seed  imperfectly 
tempered  and  they  raise  offspring  mostly  stupid,  feeble,  and  use- 
less, .  .  .  And  some  was  mixed  with  corruption .  ,  .  for  the  seed  in  that 
brew  cannot  be  rightly  raised,  it  is  invalid,  and  makes  misshapen 
men  who  are  bitter  distressed  and  oppressed  of  heart  so  that  they 
may  not  lift  their  gaze  to  higher  things. .  .  .And  often  in  forgetfulness 
of  God  and  by  the  mocking  devil  a  mistio  is  made  of  the  man  and 
the  woman  and  the  thing  born  therefrom  is  deformed,  for  parents 
who  have  sinned  against  me  return  to  me  crucified  in  their  children". 
We  have  already  traced  the  wanderings  of  the  cheese-analogy, 
which,  beginning  fresh  with  Aristotle,  was  taken  to  Alexandria  and 
incorporated  in  the  Wisdom  Literature,  and  so  found  its  way  to  the 
Arabic  of  'Ali  ibn  a'1-Abbas  al-Majusi,  or  Haly-Abbas,  as  he  was 
known  in  the  West,  a  Persian.  His  Liber  Totius  appeared  in  Latin 
in  1523,  but  had  been  translated  much  earlier,  at  Monte  Cassino 
between  1070  and  1085,  by  Constantine  the  African,  who  called  it 
Liber  de  Humana  Natura,  and  gave  it  out  to  be  his  own  work.  Thus 


(Wiesbaden  Codex  B)  showing  the  descent  of  the  soul  into  the  embryo  {ca.  1 150  a.d.). 


St  Hildegard  obtained  it,  and  worked  it  up  into  one  of  her  visions. 
At  this  point  embryology  touched,  perhaps,  its  low-water  mark.  But 
a  great  man  was  at  hand,  destined  to  carry  on  the  Aristotelian 
tradition  and  to  add  to  it  much  of  originality,  in  the  shape  of  Albertus 
of  Cologne.  Before  speaking  of  him,  however,  a  word  must  be  said 
about  that  very  queer  character,  Michael  Scot  (i  178-1234),  who, 
according  to  Gunther,  "appeared  in  Oxford  in  1230  and  experi- 
mented with  the  artificial  incubation  of  eggs,  having  got  an  Egyptian 
to  teach  him  how  to  incubate  ostriches  eggs  by  the  heat  of  the  Apulian 
sun".  That  "muddle-headed  old  magician",  as  Singer  rightly  calls 
him,  was  not  the  man  to  profit  by  it,  but  the  point  is  interesting, 
especially  as  an  Egyptian  is  mentioned.  Haskins,  in  his  curious 
studies  of  the  scientific  atmosphere  of  the  court  of  the  Emperor 
Frederick  II  of  Sicily,  has  shown  Scot,  newly  arrived  fi"om  his 
alchemical  studies  in  Spain,  assisting  that  very  learned  and  unor- 
thodox monarch  in  his  artificial  incubation  experiments. 

2-3.    Albertus  Magnus 

Albertus  Magnus  of  Cologne  and  Bollstadt  was  born  in  1206, 
and  died  in  1280,  six  years  after  his  favourite  disciple,  St  Thomas 
Aquinas.  The  greater  part  of  his  life  was  spent  in  study  and  teaching 
in  one  or  other  of  the  houses  of  the  Dominican  friars,  to  which  he 
belonged,  though  for  a  time  he  was  Bishop  of  Regensburg.  Albert 
resembles  Aristotle  in  many  points,  but  principally  because  he  pro- 
duced biological  work  with,  as  it  were,  no  antecedents.  Just  as 
Aristotle's  contributions  to  embryology  were  preceded  by  no  more 
than  the  diffuse  speculations  of  the  Ionian  nature-philosophers,  so 
Albert's  came  immediately  after  the  dead  period  represented  by  the 
visions  of  St  Hildegard.  In  many  ways,  Albert's  position  was  much 
less  conducive  to  good  work  than  Aristotle's. 

Albert  follows  Aristotle  closely  throughout  his  biological  writings, 
quoting  him  word  for  word  in  large  amounts,  but  the  significant 
thing  is  that  he  does  not  follow  him  slavishly.  He  resembled  Aristotle 
in  paying  much  attention  to  the  phenomena  of  generation,  as  a  rough 
computation  shows,  Aristotle  devoting  37  per  cent,  of  his  biological 
writings  to  this  subject,  and  Albert  31  per  cent.,  to  which  Galen's 
7  per  cent,  may  with  interest  be  compared.  Albert  is  extremely 
inferior  to  Aristotle,  however,  in  point  of  arrangement;  for  Aristotle, 
although  some  of  his  books,  such  as   the  De  Generatione  Animalium, 

98  EMBRYOLOGY  FROM  GALEN  [pt.  ii 

are  sufficiently  confused  and  repetitive,  does  yet  succeed  in  infusing 
a  clarity  and  incisiveness  into  his  style.  Albert,  on  the  other  hand, 
allows  his  argument  to  wander  through  his  twenty-six  books  De 
Animalibus  in  the  most  complex  convolutions,  so  that  the  sections  on 
generation  and  embryology  are  found  indiscriminately  in  the  first, 
sixth,  ninth,  fifteenth,  sixteenth,  and  seventeenth.  In  Book  i  he  gives 
a  kind  of  summary  or  skeleton  of  his  views  on  the  embryo.  These 
follow  Aristotle  fairly  closely;  thus,  he  accepts  the  AristoteHan  classi- 
fication of  animals  according  to  their  manner  of  generation,  and 
thinks  still  that  caterpillars  are  immature  eggs ;  he  derives  the  embryo 
from  the  white,  not  the  yolk,  and  he  explains  why  soft-shelled  eggs, 
being  imperfect,  are  of  one  colour  only.  But  there  are  new  observa- 
tions; for  instance,  he  describes  an  ovum  in  ovo,  which  he  has  seen, 
calling  it  a  natura  peccatis,  and  he  speaks  definitely  of  the  seed  of 
the  woman,  thus  departing  from  Peripatetic  opinion,  and  adopting 
the  Epicurean  view.  The  female  seed,  he  thinks,  suflfers  coagulation 
like  cheese  by  the  male  seed,  and  to  these  two  humidities  there  must 
be  added  a  third,  namely,  the  menstrual  blood  (corresponding  to 
the  yolk  in  the  case  of  the  bird).  "When  these  three  humidities 
therefore  have  been  brought  into  one  place,  all  the  similar  members 
except  the  blood  and  fat  are  formed  from  the  two  humidities  of  which 
one  generates  actively  but  the  other  passively.  But  the  blood  which  is 
attracted  for  the  nutriment  of  the  embryo  is  double  in  virtue  and 
double  in  substance.  For  a  certain  part  of  the  blood  is  united  with 
the  sperm  in  such  a  way  that  it  takes  on  some  of  the  virtue  of  the 
seed  because  a  certain  part  of  the  spermatic  humour  remains  in  it 
and  from  this  are  begotten  the  teeth  and  for  this  reason  they  grow 
again  if  they  are  pulled  out  at  an  age  near  the  time  of  sperm-making 
and  do  not  grow  again  at  an  age  remoter  from  this,  at  which  the 
virtue  of  the  first  generating  principle  has  vanished  from  the  blood. 
But  another  part  of  the  blood  is  of  twofold  or  threefold  substance 
and  from  the  thick  part  of  the  blood  itself  is  generated  the  flesh. 
And  this  flows  in  and  flows  out  and  grows  again  if  rubbed  away. 
From  the  watery  part  of  the  same  blood  or  of  the  nutritive  humour 
are  generated  the  fat  and  oil  and  this  flows  in  and  out  more  easily 
than  the  flesh  itself,  but  other  parts  of  the  blood  are  its  refuse  and 
impurities  and  are  not  attracted  to  the  generation  of  any  part  of  the 
animal,  but  having  been  collected  until  birth  are  expelled  with  the 
embryo  from  the  uterus  in  the  foetal  membranes,  like  the  remnants 


in  the  hen's  egg  after  the  chick  has  hatched.  There  is  a  similar  virtue 
in  the  liver  and  heart  of  animals  which  organs  after  the  animals  are 
born  form  the  flesh  and  fat  from  food  in  accordance  with  its  twofold 
substance,  and  expel  the  refuse  as  we  said  before," 

In  the  sixth  book,  Albert  contradicts  Aristotle's  opinion  that  male 
chick  develops  out  of  the  sharp-ended  egg,  and  one  hopes  that  he 
is  going  to  say  there  is  no  relationship  between  egg-shape  and  sex, 
but  no,  he  goes  on  to  say  that  the  Aristotelian  statement  rested  on  a 
textual  error  (in  which  he  was  quite  wrong),  so  that  really  Aristode 
agreed  with  Avicenna  in  saying  that  the  males  always  develop  from 
the  more  spherical  eggs  because  the  sphere  is  the  most  perfect  of  figures 
in  solid  geometry.  These  errors  had  a  most  persistent  life :  Horace  has 
a  passage  in  which  they  appear — 

longa  quibus  facies  ovis  erit,  ilia  memento 
ut  suci  melioris,  et  ut  magis  alma  rotundis 
ponere:  namque  marem  cohibent  callosa  vitellu.m. 

(When  you  would  feast  upon  eggs,  make  choice  of  the  long  ones ;  they 
are  whiter  and  sweeter  and  more  nourishing  than  the  round,  for  being 
hard  they  contain  the  yolk  of  the  male.) 

They  were  finally  abolished  by  two  naturalists,  Giinther  and  Biihle, 
who  took  the  trouble  to  disprove  them  experimentally  in  the  eigh- 
teenth century.  Albertus  refers  here  to  artificial  incubation:  "For 
the  alterative  and  maturative  heat",  he  says,  "of  the  egg  is  in 
the  egg  itself  and  the  warmth  which  the  bird  provides  is  altogether 
external  [extrinsecus  est  amminiculans]  since  in  certain  hot  countries 
the  eggs  of  fowls  are  put  under  the  surface  of  the  earth  and  come 
to  completion  of  their  own  accord,  as  in  Egypt,  for  the  Egyptians 
hatch  them  out  by  placing  them  under  dung  in  the  sunlight". 
Next  he  speaks  of  monsters  and  of  the  modes  of  corruption 
of  eggs  which  he  divides  into  four:  (i)  decomposition  of  white, 
(2)  decomposition  of  yolk,  (3)  bursting  of  the  yolk-membrane, 
(4)  antiquitas  ovi.  "And  from  the  second  cause  it  sometimes  happens ", 
he  says,  "that  in  the  corruption  of  the  humours  certain  igneous 
parts  are  carried  blazing  to  the  shell  of  the  egg  and  distribute  them- 
selves over  it  so  that  it  shines  in  the  dark  like  rotten  wood;  as 
happened  in  the  case  of  that  egg^  which  Avicenna  said  he  saw  in 
the  city  called  Kanetrizine  in  the  country  of  the  Gorascenes."  Albert 

^  See  on  this  subject  Zach. 



is  inclined  to  think  that  astrological  influences  may  have  an  effect 
on  foetal  life,  but  he  treats  the  suggestion  with  considerable  scepticism, 
although  he  believes  that  thunder  and  lightning  kill  the  embryos  of 
fowls  (a  popular  belief  to  which  Fere  tried  not  long  ago  to  give  a 
scientific  foundation),  and  he  regards  the  embryo  of  the  crow  as 
especially  susceptible,  though  on  what  grounds  he  does  not  say. 

The  fourth  chapter  of  the  first  tractate  of  the  sixth  book  contains 
Albert's  description  of  development  of  the  chick,  and  is  extremely 
interesting.  He  makes  two  principal  mistakes:  {a)  he  describes  a 
quite  non-existent  fissure  in  the  shell  by  which  the  chick  may  emerge, 
{b)  he  maintains  that  the  yolk  ascends  after  a  day  or  two  into  the 
sharp  end  of  the  egg,  adducing  as  the  reason  that  there  is  found 
there  more  heat  and  formative  force  than  elsewhere.  On  the  other 
hand,  he  correctly  describes  {a)  the  pulsating  drop  of  blood  on  the 
third  day,  and  {b)  he  identifies  it  with  the  heart  with  its  systolen  et 
dyastolen  sending  out  the  "formative  virtue"  to  all  the  parts  of  the 
growing  body.  He  notices  [c)  that  the  differentiation  of  the  chick  at 
first  proceeds  rapidly  and  later  more  slowly.  But  the  most  notable 
characteristic  of  Albert's  embryology  is  the  way  in  which  he  is 
hampered  by  his  inability  to  invent  a  technical  terminology.  Singer 
has  studied  the  way  in  which  anatomical  terms,  such  as  "syrach", 
etc.,  came  into  use,  but  whatever  the  causes  were  which  produced 
them,  they  did  not  operate  much  in  Albert's  mind.  He  represents 
the  point  beyond  which  embryology  could  not  advance,  until  it 
had  created  a  new  set  of  terms.  This  is  well  illustrated  by  the 
following  passage: 

"But  fi'cni  the  drop  of  blood",  he  says,  "out  of  which  the  heart  is 
formed,  there  proceed  two  vein-like  and  pulsatile  passages  and  there  is  in 
them  a  purer  blood  which  forms  the  chief  organs  such  as  the  liver  and 
lungs  and  these  though  very  small  at  first  grow  and  extend  at  last  to  the 
outer  membranes  which  hold  the  whole  material  of  the  egg  together.  There 
they  ramify  in  many  divisions,  but  the  greater  of  them  appears  on  the 
membrane  which  holds  the  white  of  the  egg  within  it  [the  allantois].  The 
albumen,  at  first  quite  white,  is  changed  owing  to  the  power  of  the  vein 
almost  to  a  pale  yellow-green  tint  [palearem  colorem].  Then  the  path  of 
which  we  spoke  proceeds  to  a  place  in  which  the  head  of  the  embryo  is 
found  carrying  thither  the  virtue  and  purer  material  from  which  are 
formed  the  head  and  the  brain,  which  is  the  marrow  of  the  head.  In 
the  formation  of  the  head  also  are  found  the  eyes  and  because  they  are  of 
an  aqueous  humidity  which  is  with  difficulty  used  up  by  the  first  heat 
they  are  very  large,  swelling  out  and  bulging  from  the  chick's  head.  A  short 


time  afterwards,  however,  they  settle  down  a  little  and  lose  their  swelling 
owing  to  the  digestive  action  of  the  heat — and  all  this  is  brought  about  by 
the  action  of  the  formative  virtue  carried  along  the  passage  which  is 
directed  to  the  head,  but  before  arriving  there  is  separated  and  ramified 
by  the  great  vein  of  the  albumen-membrane,  as  may  be  clearly  seen  by 
anyone  who  breaks  an  egg  at  this  time  and  notes  the  head  appearing  in 
the  wet  part  of  the  egg  and  at  the  top  of  the  other  members.  For  what 
appears  first  in  the  making  of  a  foetus  are  the  upper  parts  because  they  are 
nobler  and  more  spiritual  being  compacted  of  the  subtler  part  of  the  egg 
wherein  the  formative  virtue  is  stronger.  When  this  happened  one  of  the 
aforementioned  two  passages  which  spring  from  the  heart  branches  into 
two,  one  of  them  going  to  the  spiritual  part  which  contains  the  heart  and 
divides  there  in  it  carrying  to  it  the  pulse  and  subtle  blood  from  which  the 
lungs  and  other  spiritual  parts  are  formed,  and  the  other  going  through 
the  diaphragm  \dyqfracmd\  to  enclose  within  it  at  the  other  end  the  yolk 
of  the  Qgg,  around  which  it  forms  the  liver  and  stomach.  It  is  accordingly 
said  to  take  the  place  of  the  umbilicus  in  other  animals  and  through  it  food 
is  drawn  in  to  supply  the  flesh  for  the  chick's  body,  for  the  principle  of  genera- 
tion of  the  radical  members  of  the  chick  comes  from  the  albumen  but  the  food 
from  which  is  made  the  flesh  filling  up  all  the  hollows  is  from  the  yolk." 

After  ten  days,  Albert  goes  on  to  say,  all  the  constituent  organs 
are  mapped  out  and  the  head  is  greater  then  than  the  rest  of  the 
body  put  together.  He  observes  that  the  yolk  liquefies  early  in 
development  and  that  slimy  concretions  are  present  in  the  allantoic 
fluid  later  on  (uric  acid).  But  the  passage  quoted  does  demonstrate 
that  before  further  progress  could  be  made  some  better  name  must 
be  found  than  "the  interior  membrane  to  which  the  first  vessel 
proceeds"  for  a  given  structure. 

Albert,  however,  was  accomplishing  a  good  work.  One  of  his  best 
amplifications  of  Aristotle  was  his  description  of  the  relationship 
between  yolk  and  embryo  in  fishes.  Just  as  his  words  about  the  chick 
demonstrate  that  he  must  have  opened  hen's  eggs  at  different  stages 
during  incubation,  so  his  words  about  fish  eggs  show  that  he  must 
have  dissected  and  examined  them  also.  Thus  (Book  vi,  tractate  2, 
chap,  i)  he  says,  "Between  the  mode  of  development  [anathomiam 
generationis]  of  birds'  and  fishes  eggs  there  is  this  diflference ;  during 
the  development  of  the  fish  the  second  of  the  two  veins  which  extend 
from  the  heart  does  not  exist.  For  we  do  not  find  the  vein  which 
extends  to  the  outer  covering  of  the  eggs  of  birds  which  some  wrongly 
call  the  umbilicus  because  it  carries  the  blood  to  the  outside  parts, 
but  we  do  find  the  vein  which  corresponds  to  the  yolk  vein  of  birds, 
for  this  vein  imbibes  the  nourishment  by  which  the  limbs  increase. 

102  EMBRYOLOGY   FROM   GALEN  [pt.  ii 

Therefore  the  generation  of  the  fish  embryo  begins  from  the  sharp 
end  of  the  egg  like  that  of  birds  and  channels  extend  from  the  heart 
to  the  head  and  eyes  and  first  in  them  appear  the  upper  parts. 
As  the  growth  of  the  young  fish  proceeds  the  yolk  decreases  in 
amount  being  incorporated  into  the  members  and  it  disappears  en- 
tirely when  development  is  complete.  The  beating  of  the  heart,  which 
some  call  panting,  is  transmitted  through  the  pulsating  veins  to  the 
lower  part  of  the  belly  carrying  life  to  the  inferior  members.  While 
the  young  fish  are  small  and  not  yet  fully  developed  they  have  veins 
of  great  length  which  take  the  place  of  the  umbilicus,  but  as  they  grow 
these  shorten  till  they  contract  into  the  body  by  the  heart  as  has 
been  said  about  birds.  The  young  fish  are  enclosed  in  a  covering 
just  like  the  embryos  of  birds,  which  resembles  the  dura  mater  and 
beneath  it  another  containing  the  foetus  and  nothing  else,  while 
between  the  two  there  is  the  moisture  rejected  during  the  creation  of 
the  embryo".  Albert  also  described  ovoviviparous  fishes  but  it  is  more 
difficult  in  that  case  to  tell  whether  he  had  himself  seen  and  dissected 
them.  He  notes  also  the  prodigality  of  nature  in  producing  so  many 
marine  eggs  only  destined  to  be  eaten. 

In  Books  IX  and  xv  he  treats  of  the  Galenic  views  on  generation 
and  insists  again  that  there  is  a  seed  provided  by  the  female.  In 
Book  XVI  he  gives  his  opinions  about  the  animation  of  the  embryo, 
quoting  the  views  of  the  ancients  as  given  in  Plutarch,  e.g.  Alexander 
the  Peripatetic,  Empedocles,  Anaxagoras,  Theodorus  and  Theo- 
phrastus,  the  Peripatetics,  Socrates,  Plato,  the  Stoics,  Avicenna,  and 
Aristotle,  "who  saw  the  truth",  but— and  it  is  interesting  to  notice 
it — never  the  Christian  Fathers,  whose  writings  must  have  been  well 
known  to  him.  In  discussing  the  Aristotelian  views  he  compares  the 
menstrual  blood  to  the  marble  and  the  semen  to  the  man  with  a 
chisel  in  his  hand. 

On  the  question  of  epigenesis  and  preformation,  he  follows 
Aristotle  almost  word  for  word,  using  the  same  analogies,  such  as 
the  "dead  eye"  and  the  sleeping  mathematician.  Here  his  scho- 
lasticism comes  out  clearly,  for  in  rejecting  altogether  the  theory 
that  one  part  being  formed  then  forms  the  next  part,  he  says,  not 
that  A  would  have  to  be  in  some  way  like  B,  but  is  not,  as  Aristotle 
had,  but  simply  "^Generans  et  generatum,  est  simul  esset  et  non  esset, 
quod  omnino  est  impossibile''^ — a  high-handed  and  very  unscientific 
manner  of  settling  the  question.   In  conformity  with  his  theology  and 

SECT.  2]  TO   THE    RENAISSANCE  103 

in  contradistinction  from  Aristotle  he  makes  the  vegetative  and 
sensitive  souls  arrive  automatically  into  the  embryo  but  the  rational 
soul  only  by  a  direct  act  of  God. 

His  mammalian  embryology  presents  some  points  of  interest.  He 
follows  Hippocrates  ("Ypocras")  in  an  account  of  the  co-operation 
of  heat  and  cold  in  member-formation,  and  he  holds  very  enlightened 
views  about  foetal  nutrition,  "It  appears  therefore  that  the  embryo 
hangs  from  the  cord  and  that  the  cord  is  joined  with  the  vein  and 
that  the  vein  extends  through  the  uterus  and  has  blood  running 
through  it  to  the  foetus  like  water  through  a  canal.  Round  the  embryo 
there  are  membranes  and  webs  as  we  have  seen.  But  those  who  think 
that  the  embryo  is  fed  by  little  bits  of  flesh  through  the  cord  are 
wrong  and  lie,  because  if  this  were  the  case  with  man  it  would  happen 
also  with  other  animals  and  that  it  does  not  do  so  anybody  can  find 
out  by  investigation  [per  anathomyani].'" 

Finally,  it  is  typical  that  in  Book  xvii  Albert  repeats  what  he  has 
already  said  in  Book  vi  about  the  generation  of  the  hen  out  of  the 
tgg  all  over  again  with  slight  changes,  but  he  adds  the  significant 
biochemical  remark  that  "eggs  grow  into  embryos  because  their 
wetness  is  like  the  wetness  of  yeast".  The  importance  of  Albert  in 
the  history  of  embryology  is  clear.  With  him  the  new  spirit  of  in- 
vestigation leapt  up  into  being,  and,  though  there  were  many  years 
yet  to  pass  before  Harvey,  the  modern  as  opposed  to  the  ancient 
period  of  embryology  had  begun.  Albert's  writings  were  often 
copied  and  printed  in  the  next  few  centuries,  and  even  as  late  as  1601 
De  Secretis  Mulierum,  an  epitome  of  his  books  on  generation,  was 
published.  In  some  sense,  it  still  is,  as  it  forms  the  backbone  of  the 
little  book  Aristotle's  Masterpiece,  of  which  thousands  of  copies  are  sold 
in  England  every  year.  The  copy  of  the  De  Secretis  in  the  Caius  College 
Library  has  written  across  the  title-page  in  faded  ink  "Simulacra 
sanctitas,  duplex  iniquitas,  Nathan  Emgross,  Nov.  20.  161 3."  But  in 
spite  of  Mr  Emgross,  Albertus,  rightly  called  Magnus,  has  had  the 
happy  fate  of  being  beatified  both  by  the  Church  and  by  science. 

2-4.    The  Scholastic  Period 

St  Thomas  Aquinas  (i  227-1 274)  incorporated  the  Aristotelian 
theories  of  embryology  into  his  Summa  Theologica  especially  under 
the  head  De  propagatione  hominis  quantum  ad  corpus.  There  are  some 
striking  passages,  such   as   "The   generative  power  of  the  female 

104  EMBRYOLOGY  FROM  GALEN  [pt.  ii 

is  imperfect  compared  to  that  of  the  male;  for  just  as  in  the  crafts, 
the  inferior  workman  prepares  the  material  and  the  more  skilled 
operator  shapes  it,  so  likewise  the  female  generative  virtue  provides 
the  substance  but  the  active  male  virtue  makes  it  into  the  finished 
product".  How  admirably  this  expresses  the  dominating  sentiment 
of  the  Middle  Ages!  Aristotle  might  make  a  distinction  between 
matter  and  form  in  generation,  but  the  mediaeval  mind,  with  its 
perpetual  hankering  after  value,  would  at  once  enquire  which  of  the 
two  was  the  higher,  the  nobler,  the  more  honourable. 

St  Thomas'  theory  of  embryonic  animation  was  complicated.  He 
had  a  notion  that  the  foetus  was  first  endowed  with  a  vegetative 
soul,  which  in  due  course  perished,  at  which  moment  the  embryo 
came  into  the  possession  of  a  sensitive  soul,  which  died  in  its  turn, 
only  to  be  replaced  by  a  rational  soul  provided  directly  by  God, 
This  led  him  into  great  difficulties,  for,  if  this  scheme  were  true,  it 
was  difficult  to  say  that  man  generated  man  at  all;  on  the  contrary 
he  could  hardly  be  said  to  generate  more  than  a  sensitive  soul  which 
died  before  birth,  and,  on  this  view,  what  was  to  happen  to  original 
sin?  As  Harris  has  put  it,  Plato  had  said  that  the  intellect  was  the 
man,  using  the  body  as  a  boatman  uses  a  boat.  Averroes  had  said 
precisely  the  opposite,  namely,  that  the  essence  of  humanity  was  in 
the  body,  and  that  the  intellect  was  something  extrinsic,  not  limited 
to  the  individual,  but  common  to  the  race.  Aristotle  had  taken  the 
middle  position,  and  given  a  soul  to  plants  and  animals,  but,  in 
doing  so,  he  had  made  it  into  a  vital  rather  than  a  psychological 
principle.  The  task  of  combining  this  -^vxv  with  the  anima  of  the 
Fathers  was  what  scholastic  philosophy  had  before  it.  No  wonder 
that  St  Thomas'  account  of  embryonic  animation  was  open  to 
criticism.  An  echo  of  it  appears  in  a  poem  of  Jalalu'd-Din  Rumi 
( 1 207-1 273),  the  greatest  of  the  Persian  Sufi  poets,  and  an  exact 
contemporary  of  St  Thomas  Aquinas : 

I  died  from  mineral  and  plant  became: 
Died  from  the  plant,  and  took  a  sentient  frame; 
Died  from  the  beast,  and  donned  a  human  dress; 
When  by  my  dying  did  I  e'er  grow  less? 

Duns  Scotus  (i  266-1 308)  objected  to  St  Thomas'  theory  on  the 
grounds  already  mentioned,  and  he  himself  abandoned  the  vegetative 
and  sensitive  souls  altogether  in  his  De  Rerum  Principio.  This  solution 


was  no  better  than  that  of  St  Thomas,  for,  agreeing  with  the  latter 
as  Duns  did  that  the  rational  soul  was  not  an  ordinary  form  "educed " 
from  the  "potentiality"  of  the  material,  but  rather  an  ad  hoc  creation 
of  God,  injected  by  divine  power  into  the  embryo  at  the  appropriate 
moment,  it  was  difficult  to  see  how  the  spiritual  effects  of  Adam's 
fall  could  be  transmitted  to  the  men  of  each  generation.  It  was  as 
if  only  acquired  characteristics  were  inherited.  But  the  further  course 
of  theological  embryology  need  not  be  pursued  here ;  it  runs  in  every 
century  parallel  with  true  scientific  embryology,  and  it  is  not  my 
purpose  to  do  more  than  take  a  glance  at  its  progress  from  time  to  time. 
In  the  Speculum  Naturale,  which  was  written  about  1250,  by  Vincent 
of  Beauvais,  the  embryology  of  Constantine  the  African  appears 
again,  and  the  embryology  of  Aristotle,  Galen,  and  the  scholastics 
is  to  be  found  in  Dante  Alighieri  (i 265-1 321),  who  dealt  with  the 
subject  in  his  Convivio,  and  especially  in  the  Divina  Commedia.  In 
Canto  XXV  of  the  Purgatorio,  Statins  (the  personification  of  human 
philosophy  enlightened  by  divine  revelation)  is  made  to  speak  to 
the  poet  thus:  "If  thy  mind,  my  son,  gives  due  heed  to  my  words 
and  takes  them  home,  they  will  elucidate  the  question  thou  dost  ask. 
Perfect  blood  which  is  in  no  case  drawn  from  the  thirsty  veins,  but 
which  remains  behind  like  food  that  is  removed  from  table,  receives 
in  the  heart  informing  power  for  all  the  members  of  the  human  body, 
like  the  other  blood  which  courses  through  the  veins  in  order  to  be 
converted  into  those  members.  After  being  digested  a  second  time 
it  descends  to  the  part  whereof  it  is  more  seemly  to  keep  silence  than 
to  speak,  and  thence  it  afterwards  drops  into  the  natural  receptacle 
(the  uterus)  upon  another's  blood ;  there  the  one  blood  and  the  other 
mingle.  One  is  appointed  to  be  passive,  the  other  to  be  active 
according  to  the  perfect  place  whence  it  proceeds  (the  heart).  And 
being  united  with  it,  it  begins  to  operate,  first  by  coagulating  it,  and 
then  by  vivifying  that  to  which  it  has  given  consistency,  so  that  there 
may  be  material  for  it  to  work  upon  [e  poi  avviva,  Cib  che  per  sua  materia 
fe'  constare].  The  active  power  having  become  a  (vegetative)  soul  like 
that  of  a  plant — only  differing  from  it  in  this,  that  the  former  is  in 
progress  while  the  latter  has  reached  its  goal — thereafter  works  so 
much  that  it  moves  and  feels  like  a  sea-fungus  and  as  the  next  stage 
it  takes  in  hand  to  provide  with  organs  the  faculties  which  spring 
from  it.  At  this  point,  my  son,  the  power  which  proceeds  from  the 
heart  of  the  begetter  is  expanded  and  developed,  that  power  in  which 

io6  EMBRYOLOGY   FROM   GALEN  [pt.  ii 

Nature  is  intent  on  forming  all  the  members,  but  how  from  being 
an  animal  it  becomes  a  child,  thou  seest  not  yet,  moreover  this  is 
so  difficult  a  point  that  formerly  it  led  astray  one  more  wise  than  thou 
[Averroes],  so  that  in  his  teaching  he  separated  the  active  'intellect' 
from  the  soul  because  he  could  not  see  any  organ  definitely  appro- 
priated by  it.  Open  thy  heart  to  the  truth  and  know  that  as  soon 
as  the  brain  of  the  foetus  is  perfectly  organised,  the  Prime  Mover, 
rejoicing  in  this  display  of  skill  on  the  part  of  Nature,  turns  him 
towards  it  and  infuses  a  new  spirit  replete  with  power  into  it  which 
subsumes  into  its  own  essence  the  active  elements  which  it  finds  al- 
ready there,  and  so  forms  one  single  soul  which  lives  and  feels  and 
is  conscious  of  its  own  existence.  And  that  thou  mayst  find  my  saying 
less  strange,  bethink  thee  how  the  heat  of  the  sun  passing  into  the 
juice  which  the  grape  distils,  makes  wine". 

Having  said  this.  Statins,  Virgil  and  Dante  pass  on  to  the  seventh 
ledge  in  Purgatory.  It  is  interesting  to  see  how  Dante  emphasises 
the  dynamic  teleological  side  of  Aristotle  and  practically  speaks  of 
the  soul  enfleshing  itself  and  arranging  organs  for  its  faculties.  The 
reference  to  Averroes  is  explained  by  the  fact  that  Averroes  was  a 
Traducianist,  and  held  that  all  the  soul  was  generated  by  man  at 
the  same  time  as  the  body,  whereas  both  St  Thomas  and  Dante,  as 
Creationists,  held  that  each  fresh  soul  was  a  special  creation  of  God 
inserted  by  him  into  the  brain  of  the  embryo.  The  mention  of  Dante's 
contemporary,  Mondino  de  Luzzi  (1270-1326),  brings  us  to  the  more 
practical  aspects  of  embryology  at  this  period.  Mondino  is  the  most 
outstanding  figure  among  the  Bolognese  anatomists  of  what  is  really 
the  first  period  of  the  revival  of  biology.  After  him,  as  we  shall  see, 
biology  languished  for  a  couple  of  centuries  until  the  advent  of  such 
men  as  Ulysses  Aldrovandus  in  the  sixteenth  century,  and  Singer  has 
shown  that  this  was  probably  due  to  the  fact  that  anatomy  professors 
did  not  dissect  in  person.   A  fortiori  embryotomy  was  infrequent. 

But  Mondino's  Anathomia,  published  in  13 16,  contained  statements 
about  the  organs  of  generation  which  were  rather  important.  He 
retains  the  notion  of  the  seven-celled  uterus,  which  had  been  intro- 
duced by  Michael  Scot,  but  he  adopts  a  reasonable  compromise 
between  the  opinions  of  Galen  and  Aristotle  on  the  physiology  of 
embryo  formation.  The  distance  between  him  and  Leonardo  da 
Vinci  (1452-1519)  would,  however,  be  estimated  rather  at  five  or  six 
centuries  than  at  the  century  and  a  quarter  that  it  actually  was. 


2-5.    Leonardo  da  Vinci 

Leonardo  was  not  alone  among  the  artists  of  the  Renaissance  in 
his  anatomical  interests,  for  Michael  Angelo,  Raphael,  Diirer, 
Mantegna,  and  Verrochio  all  made  dissections  in  order  to  increase 
their  knowledge  of  the  human  body.  But  he  penetrated  more  curiously 
into  biology  than  they  did,  and  he  will  always  remain  one  of  the 
greatest  of  biologists,  for  he  first  introduced  the  quantitative  outlook. 
In  this  he  was  some  four  hundred  years  before  his  time. 

Leonardo's  embryology  is  contained  in  the  third  volume  of  his 
notebooks,  Quaderni  d'  Anatomia,  published  in  facsimile  by  the  ad- 
mirable labours  of  three  Norwegian  scholars,  Vangensten,  Fohnahn 
and  Hopstock,  in  191 1.  His  notebooks  are  a  remarkable,  and,  indeed, 
charming  miscellany  of  anatomical  drawings,  physiological  diagrams, 
architectural  and  mechanical  sketches  and  notes  such  as  "Shirts, 
hose,  and  shoes",  "Go  and  see  Messer  Andreas",  "get  coal",  "the 
supreme  fool  (is  the)  necromancer,  and  enchanter". 

His  dissections  of  the  pregnant  uterus  and  its  membranes  are 
beautifully  depicted,  as  can  be  seen  from  the  figures  which  are  here 
reproduced  (Plate  IV).  He  was  acquainted  with  amnios  and  chorion, 
and  he  knew  that  the  umbilical  cord  was  composed  only  of  vessels, 
though  he  seems  to  have  thought  the  human  placenta  was  cotyle- 
donous.  There  is  one  drawing  which  the  editors  suppose  to  represent 
the  developing  hen's  egg,  but  I  do  not  feel  that  this  ascription  is  likely. 
Indeed,  Leonardo  worked  with  eggs  much  less  than  with  mammalian 
embryos,  though  there  are  references  to  the  former.  "See  how  birds 
are  nourished  in  their  eggs",  he  says  in  one  place,  to  remind  himself, 
perhaps,  of  possible  experiments,  and,  elsewhere,  "Chickens  are 
hatched  by  means  of  the  ovens  of  the  fireplace".  Again,  "Ask  the 
wife  of  Biagino  Crivelli  (was  she  the  Lucrezia  Crivelli,  whose  portrait 
Leonardo  painted?)  how  the  capon  rears  and  hatches  the  eggs  of  the 
hen  when  he  is  inebriated",  a  subject  recently  reopened  by  Lienhart. 
"You  must  first  dissect  the  hatched  egg  before  you  show  the  difference 
between  the  human  liver  in  foetus  and  adult."  Leonardo  perpetuates 
a  persistent  error  in  the  note,  "Eggs  which  have  a  round  form 
produce  males,  those  which  have  a  long  form  produce  females". 

Concerning  the  mammalian  foetus,  he  says,  "The  veins  of  the 
child  do  not  ramify  in  the  substance  of  the  uterus  of  its  mother  but 
in  the  placenta  which  takes  the  place  of  a  shirt  in  the  interior  of  the 

io8  EMBRYOLOGY  FROM  GALEN  [pt.  ii 

uterus  which  it  coats  and  to  which  it  is  connected  but  not  united  by 
means  of  the  cotyledons".  Thus  in  one  sentence  Leonardo  falls  into 
a  mistake  in  saying  that  the  human  placenta  is  cotyledonous,  but 
at  the  same  time  asserts  a  fact  which  it  took  all  the  ingenuity  of  the 
seventeenth  century  to  prove  to  be  true,  namely,  that  the  foetal 
circulation  is  not  continuous  with  that  of  the  mother,  for  the  placenta 
is  only  connected  to  the  uterine  wall  and  not  united  with  it.  "The 
child",  Leonardo  goes  on  to  say,  "lies  in  the  uterus  surrounded  with 
water,  because  heavy  things  weigh  less  in  water  than  in  the  air 
and  the  less  so  the  more  viscous  and  greasy  the  water  is.  And  then 
such  water  distributes  its  own  weight  with  the  weight  of  the  creature 
over  the  whole  body  and  sides  of  the  uterus."  The  tendency  towards 
quantitative  and  mathematical  explanations  is  apparent  at  once. 

Further  notes  are,  "Note  how  the  foetus  breathes  and  how  it  is 
nourished  through  the  umbilical  cord  and  why  one  soul  governs  two 
bodies,  as  you  see  the  mother  desiring  food  and  the  child  remaining 
marked  (by  a  given  amount  of  growth)  because  of  it.  Avicenna 
pretends  that  the  soul  generates  the  soul  and  the  body  the  body. 
Per  errata^'.  The  child,  says  Leonardo,  secretes  urine  while  still  in 
utero,  and  has  excrement  in  its  intestines;  at  four  months  it  has  chyle 
in  its  stomach,  made  perhaps  from  menstrual  blood.  But  it  has  no 
voice  in  utero,  "when  women  say  that  the  foetus  is  heard  to  weep 
sometimes  within  the  uterus,  this  is  rather  the  sound  of  some  flatus . .  . ". 
Nor  does  it  breathe  there  (on  this  point  Leonardo  contradicts  him- 
self). "The  child  does  not  respire  within  the  body  of  its  mother 
because  it  lies  in  water  and  he  who  breathes  in  water  is  immediately 
drowned."  "Breathing  is  not  necessary  to  the  embryo  because  it  is 
vivified  and  nourished  by  the  life  and  food  of  the  mother."  Nor  does 
the  embryonic  heart  beat.  To  us  the  statement  that  there  is  no 
respiration  in  the  uterus  is  obviously  false,  but  we  mean  by  the  word 
tissue  respiration,  whereas  in  Leonardo's  time  pulmonary  respiration 
was  intended;  he  was  therefore  perfectly  right  in  denying  that  the 
embryo  breathed,  as  certain  anatomists  before  him  had  asserted. 

His  only  reference  to  the  soul  runs  thus:  "Nature  places  in  the 
bodies  of  animals  the  soul,  the  composer  of  the  body,  i.e.  the  soul 
of  the  mother,  which  first  composes,  in  the  womb,  the  shape  of  man 
and  in  due  time  awakens  the  soul  which  shall  be  the  inhabitant  there- 
of, which  first  remains  asleep  and  under  the  tutelage  of  the  soul  of 
the  mother  which  through  the  umbilical  vein  nourishes  and  vivifies 


vf  Hi^l 


O       V^xf^rtl 

V-..,'.'.^/  I   »-^  '•' 

•V     'j'.'/**    •»T^'"('   ''♦' 

{QUADERNI  D'  ANATOMIA),  ca.  1490  a.d. 


it".  This  is  not  very  revolutionary.  But  Leonardo  was  the  first 
embryologist  to  make  any  quantitative  observations  on  embryonic 
growth ;  he  defined,  for  instance,  the  length  of  a  full-grown  embryo 
as  one  braccio  and  the  adult  as  three  times  that.  "The  child",  he 
says,  "grows  daily  far  more  when  in  the  body  of  its  mother  than 
when  it  is  outside  of  the  body  and  this  teaches  us  why  in  the  first 
year  when  it  finds  itself  outside  the  body  of  the  mother,  or,  rather, 
in  the  first  9  months,  it  does  not  double  the  size  of  the  9  months 
when  it  found  itself  within  the  mother's  body.  Nor  in  18  months 
has  it  doubled  the  size  it  was  9  months  after  it  was  born,  and  thus 
in  every  9  months  diminishing  the  quantity  of  such  increase  till 
it  has  come  to  its  greatest  height."  Here  Leonardo  touches  on  one 
of  the  most  modern  quantitative  aspects  of  embryology,  and  one 
almost  expects  to  see  him  exemplify  his  words  with  a  graph  until 
one  remembers  with  a  shock  that  he  lived  two  centuries  before 
Descartes  and  five  before  Minot.  His  numerical  data  may  also  have 
included  figures  about  the  relative  sizes  of  the  parts,  and  the  germ 
of  the  line  of  research  so  successfully  pursued  by  Scammon  in  our 
own  times  may  be  found  in  the  note  "The  liver  is  relatively  much 
larger  in  the  foetus  than  in  the  grown  man".  Other  quantitative 
notes  concern  the  length  of  the  embryonic  intestines  as  in  the  laconic 
"20  braccia  of  bowels"  and  the  statement  that  "the  length  of  the 
umbilical  cord  always  equals  the  length  of  the  foetal  body  in  man 
though  not  in  animals".^ 

He  said  little  about  heredity,  but  in  one  place  he  mentions  a  case 
of  sexual  intercourse  between  an  Italian  woman  and  an  Ethiopian, 
the  outcome  of  which  assured  him  that  blackness  was  not  due  to  the 
direct  action  of  the  sun  and  that  the  "seed  of  the  female  was  as  potent 
as  that  of  the  male  in  generation".  Finally,  the  best  instance  of  the 
wideness  of  his  thought  appears  in  the  note,  "All  seeds  have  an  um- 
bilical cord  which  breaks  when  the  seed  is  mature.  And  similarly 
they  have  matrix  and  secundines  as  the  herbs  and  all  the  seeds 
which  grow  in  shells  show".  We  have  met  this  idea  before  in  Hippo- 
crates of  Cos,  and  we  shall  find  it  again  in  Nathaniel  Highmore. 

It  is  no  coincidence  that  pictures  of  weights  and  cogs  and  pulleys 
stand  side  by  side  in  Leonardo's  notes  with  anatomical  drawings  of 
the  embryo.  As  Hopstock  says,  "Leonardo  arrives  at  the  conclusion 
that  there  is  but  one  natural  law  which  governs  the  world.  Necessity. 

^  Leonardo  would  have  enjoyed  Fog's  statistical  study  of  8000  umbUical  cords  (1930). 

no  EMBRYOLOGY   FROM   GALEN  [pt.  ii 

Necessity  is  Nature's  master  and  guardian,  it  is  Necessity  that  makes 
the  eternal  laws".  If  Aristotle  is  the  father  of  embryology  regarded 
as  a  branch  of  natural  history,  Leonardo  is  the  father  of  embryology 
regarded  as  an  exact  science. 

2-6.    The  Sixteenth  Century:  the  Macro- Iconographers 

After  such  a  man,  the  writings  of  his  contemporaries,  such  as  the 
mythical  Johannes  de  Ketham,  Alessandro  Achillini  and  Gabriele  de 
Gerbi,  appear  beyond  description  inferior.  De  Ketham's  embryology 
has  been  described  by  Ferckel.  De  Gerbi  included  in  his  Liber 
Anatomiae  corporis  humani  et  singulorum  membrorum  illius  a  section 
entitled  De  Generatione  Embrjonis,  but  there  is  nothing  to  be  said 
about  it  except  that  it  is  a  verbose  compilation  of  the  views  of 
Aristotle  and  Galen  taken  from  Avicenna.  The  work  of  Nolanus  in 
1532  presents  certain  points  of  interest,  but  it  is  of  little  importance. 
Petrus  Crescentius  in  his  work  on  husbandry  of  1548  mentions 
artificial  incubation  in  ovens,  but  rather  as  a  lost  art.  About  this 
time  also  Hieronymus  Dandinus  Cesenas,  a  Jesuit,  wrote  a  treatise 
on  Galen's  division  of  organs  into  white  and  red,  those  proceeding 
from  the  semen  and  those  proceeding  from  the  blood:  it  is  cited  by 
Aldrovandus,  but  I  have  not  been  able  to  consult  it. 

The  most  remarkable  feature  of  the  first  half  of  the  century  was 
the  encyclopaedic  group  of  zoologists  which  now  arose.  Thus  Belon 
and  Rondelet,  whose  well-illustrated  catalogues  of  animals  were 
appearing  from  1550  onwards,  did  a  good  service  to  comparative 
embryology  in  figuring  the  ovoviviparous  selachians  and  viviparous 
cetacea.  Gesner  belongs  to  this  group.  All  of  them  reproduce  thin 
versions  of  Aristotle,  when  they  speak  of  generation  as  such,  and  this 
is  what  differentiates  them  from  Ulysses  Aldrovandus,  of  whom  I 
shall  speak  presently.  Figs.  3  and  4  show  Rondelet's  pictures  of  a 
viviparous  dolphin  and  an  ovoviviparous  selachian. 

But  the  end  of  the  twilight  period  was  now  at  hand,  for,  within 
thirty  years  after  the  death  of  de  Gerbi  in  1505,  four  great 
embryologists  were  born  as  well  as  the  greatest  anatomist  of  any  age, 
Andreas  Vesalius  (1514),  of  whom  I  shall  say  no  more,  for  he  had 
no  opportunities  for  dissecting  human  embryos,  and  took  hardly 
any  interest  in  foetal  development.  But  in  1522  Ulysses  Aldrovandus 
was  born,  and  in  the  following  year  Gabriel  Fallopius,  in  1530 
Julius  Caesar  Arantius  and  in   1534  Volcher  Goiter.    Only  three 

SECT.  2] 



more  years  bring  us  to  the  birth  of  Andreas  Laurentius  and  of 
Hieronymus  Fabricius  ab  Aquapendente,  the  teacher  of  William 

The  senior  member  of  this  group,  Ulysses  Aldrovandus,  was  the 
first  biologist  since  Aristotle  to  open  the  eggs  of  hens  regularly  during 

Fig.  3.   A  (viviparous)  dolphin:  from  Rondelet's  De  piscibus  marinis  of  1554. 

their  incubation  period,  and  to  describe  in  detail  the  appearances 
which  he  found  there.  In  his  Ornithologia,  published  at  Bonn  in  1597, 
he  set  out  to  describe  all  the  known  kinds  of  birds,  discussing  in 
turn  not  only  their  zoological  and  physiological  characteristics,  but 

Fig.  4.  An  (ovoviviparous)  shark:  from  Rondelet's  De  piscibus  marints  of  1554. 

also  their  significance  as  presages  and  for  augury,  their  mystical 
meaning,  their  use  as  allegories  and  for  eating,  and  finally  all  the 
legends  respecting  them,  Generositas,  Temperantia,  Liberalitas,  aquilae 
one  finds.  Beginning  with  the  eagle,  he  proceeds  to  the  vulture, 
the  owl,  the  bat  (the  only  viviparous  bird!),  the  ostrich,  the  harpy (!), 

112  EMBRYOLOGY   FROM   GALEN  [pt.  ii 

the  parrot,  the  crow,  and  so  to  the  fowl.  Side  by  side  with  a 
reference  to  the  famous  poem  of  Prudentius  {Multi  sunt  Presbyteri, 
translated  by  J.  M.  Neale)  about  the  steeple-cock,  we  find  an 
excellent  account  of  the  generation  of  the  chick  in  the  c:gg.  The  book 
is  illustrated  sumptuously,  but  unfortunately  there  is  only  one  picture 
of  embryological  interest,  namely,  a  chick  in  the  act  of  hatching. 

In  Aldrovandus'  embryology  there  is  much  discussion  of  Aristotle 
and  Galen,  but  traces  of  an  independent  spirit  abound.  Pliny's  view 
that  the  heart  was  formed  in  the  white  is  "exploded",  and  Aldro- 
vandus says  that  it  is  formed  on  the  yolk-membrane.  He  refutes  the 
opinion  of  Galen  also  that  the  liver  is  first  formed,  in  connection 
with  which  he  says,  "In  order  that  I  might  bring  to  an  end  this 
controversy  between  the  philosophers  and  the  physicians  I  followed 
with  the  keenest  curiosity  and  diligence  the  incubation  of  22  hen's 
eggs,  opening  one  each  day;  thus  I  found  Aristotle's  doctrine  to  be  the 
truest.  And  because  apart  from  the  fact  that  these  matters  are  most 
worthy  of  being  looked  into  they  provide  also  the  greatest  pleasure 
and  entertainment  I  have  thought  it  well  to  describe  them  as  clearly 
and  briefly  as  possible". 

Aldrovandus  also  contradicts  Albertus,  and  propounds  a  new 
theory,  namely,  that  the  spiritualia  (the  organs  in  the  thorax)  are 
formed  from  the  seed  of  the  cock  {ex  maris  semine  sunt).  This  seed 
he  aflfirms  to  be  present  in  the  egg,  and  he  identifies  it  with  the 
chalazae,  thus  anticipating  Fabricius  ab  Aquapendente,  but  not 
going  quite  so  far,  and  explicitly  opposing  Gaza,  who  had  said  not 
long  before  that  the  chalazae  were  simply  congealed  water.  Aldro- 
vandus' admiration  for  Aristotle  is  extreme,  and,  though  he  differs 
from  him  about  the  chalazae,  he  defends  the  Aristotelian  opinion 
that  the  chick  was  made  from  the  white  but  nourished  from  the  yolk. 
His  argument  for  this  is  new,  however;  it  is  that,  during  incubation, 
the  latter  liquefies  but  the  former  hardens;  now  in  all  digestion 
liquefaction  takes  place,  and  in  all  growth  hardening,  therefore,  etc. 
This  argument  is  a  great  deal  more  cogent  than  most  of  those  which 
were  current  between  1550  and  1650.  He  goes  out  of  his  way  to 
castigate  Albertus  for  saying  that  the  yolk  moves  up  into  the  sharp 
point  of  the  egg,  for  experience  assures  him  that  it  does  not,  "as  I 
have  observed  by  cutting  open  an  egg  after  one  day's  incubation". 
A  striking  instance  of  his  powers  of  observation  was  his  description 
of  the  "egg-tooth"  of  embryonic  birds,  a  discovery  made  anew  in 


the  nineteenth  century  by  Yarrell  and  Rose.  The  chick  was  perfect 
in  form,  according  to  him,  on  the  tenth  day. 

The  peculiarity  of  Aldrovandus  lies  in  the  fact  that  he  incorporated 
so  many  elements  into  one  book,  and  was  able  to  produce  a  collection 
of  chapters  in  which  good  scientific  observation  sat  at  the  closest 
quarters  with  literary  allusion  and  semi-theological  homily.  So  well- 
proportioned  a  mixture  as  the  Ornithologia  is  not  often  found.  As  a 
final  instance  three  consecutive  paragraphs  may  be  mentioned,  in 
the  first  of  which  he  discusses  Plutarch's  arid  problem  about  the 
priority  of  egg  or  hen,  next  he  makes  some  very  reasonable  remarks 
about  teratology,  suggesting  that  monsters  come  from  yolks  which  are 
physico-chemically  abnormal  in  some  way,  while  in  the  third  he 
expresses  strong  scepticism  concerning  the  tale  that  the  basilisk  is 
sometimes  hatched  out  from  a  hen's  egg — ''Ego  ne  jurantibus  quidem 
crediderim'\  he  says.  This  last  notion  is  found  in  the  fourteenth- 
century  poem  of  Prudentius  alluded  to  above,  and  appears  again  in 
the  Miscellaneous  Exercitations  of  Caspar  Bartholinus  the  younger, 
whose  second  chapter  is  devoted  to  showing  "That  the  basilisk 
hatcheth  not  from  the  egg  of  the  hen",  a  conclusion  which  has  been 
amply  confirmed  in  the  light  of  subsequent  experience.  Bartholinus 
gives  a  bibliography  of  this  curious  legend. 

Aldrovandus  and  his  disciple  Volcher  Coiter  the  Frisian,  as  he 
described  himself,  were  alike  in  not  suffering  from  the  prevailing 
vice  of  the  age,  verbosity.  Colter's  Externarum  et  Internarum  princi- 
palium  humajii  corporis  partium  tabulae  et  exercitationes,  which  appeared 
at  Nuremberg  in  1573 — a  beautifully  printed  book — contained  a 
brief  section  entitled  De  ovorum  gallinaceorum  generationis  primo  exordio 
progressuque  et  pulli  gallinacei  creationis  ordine.  His  Latin  style  betrays 
his  German  origin,  for  the  constructions  are  very  Teutonic,  although 
the  meaning  is  always  perfectly  clear.  Coiter  says,  "In  the  year 
1564  in  the  month  of  May  at  Bologna,  being  instigated  by  that 
excellent  professor  of  philosophy  outstanding  in  varied  sciences  and 
arts.  Doctor  Ulysses  Aldrovandus,  and  by  other  doctors  and  students, 
I  ordered  2  broody  fowls  to  be  brought  and  under  each  of  them 
I  caused  23  eggs  to  be  placed,  and  in  the  company  of  these  persons 
I  opened  one  every  day  so  that  we  could  see  firstly  the  origin  of 
the  veins  and  secondly  what  organ  is  first  formed  in  the  animal". 
What  follows  is  practically  a  repetition  of  the  facts  available  in 
Aristotle,  but  described  with  much  greater  clearness  than  either 

114  EMBRYOLOGY  FROM   GALEN  [pt.  ii 

Aristotle  or  Aldrovandus  had  been  able  to  bring  to  the  matter. 
On  the  third  day,  he  saw  the  globulus  sanguineus  which  in  vitello 
manifeste  pulsabat,  and  so  solved  his  first  problem.  He  decides  that 
the  first  organ  to  be  formed  is  the  heart,  and  quotes  Lactantius' 
experiments.  He  explains  the  large  size  of  the  eye  as  due  to  the  fact 
that  the  most  complicated  part  of  the  body  needs  the  longest  time 
for  its  manufacture.  He  correctly  describes  the  various  membranes, 
and  the  faeces  subviridies  in  the  intestines  at  hatching.  Once  he 
contradicts  Aristotle,  maintaining  that  on  the  tenth  day  the  body  as 
a  whole  is  larger  than  the  head,  and  once  he  contradicts  Albertus, 
denying  that  any  yolk  can  be  found  in  the  stomach  at  hatching.  He 
concludes  his  tractate  by  a  succinct  and  clear  account  of  the  opinions 
of  Aristotle  and  Hippocrates  about  embryonic  development.  His 
importance  is  that  he  drew  the  attention  of  scientific  thinkers  to  the 
problems  arising  out  of  the  hen's  egg,  and  assisted  in  the  formation 
of  that  iconographic  phase  in  embryology  which  was  later  to  find 
its  climax  in  the  plates  of  Fabricius,  and  its  close  in  Harvey's  Exer- 

Gabriel  Fallopius,  who  belongs  to  this  time,  must  be  mentioned 
as  the  discoverer  of  the  organs  which  bear  his  name,  but  his  services 
to  embryology  were  only  indirect.  A.  Benedictus,  who  was  now 
growing  old,  and  Caesar  Cremonius,  who  was  still  young,  may  be 
remembered  as  the  principal  upholders  of  pure  Aristotelianism  at  this 
time.  Realdus  Columbus  also  wrote  on  the  embryo.  B.  Telesius, 
in  his  De  Natura  Rerum  of  1565,  studied  the  hen's  egg  and  suggested 
that  the  parts  of  animals  were  formed  by  the  pressure  of  the  uterus 
acting  as  a  mould:  he  was  thus  the  middle  term  between  Galen 
and  Buffon. 

Julius  Caesar  Arantius  has  already  been  referred  to.  His  De 
Humano  Foetu  was  an  important  book,  but,  though  it  appeared  in 
1564,  just  at  the  time  when  the  macro-iconographic  school  was  at 
its  height,  it  dealt  with  a  rather  different  field  and  cannot  be  con- 
sidered as  a  constituent  of  that  group.  He  begins  by  relating  that  a 
pregnant  woman  was  killed  by  an  accident  at  Bologna  a  couple  of 
years  before,  so  that  he  had  an  opportunity  of  testing  whether  the 
opinions  about  certain  points  in  generation,  which  he  had  formed 
on  a  priori  grounds  during  the  previous  fifteen  years,  were  true  or 
not.  In  the  first  place,  he  found  on  dissection  that  the  placenta  was 
not  cotyledonous,  and  he  spoke  thus  of  its  formation:  "Blood  flows 


out  from  the  spongy  substance  of  the  uterus  and  this  blood  growing 
in  bulk  forms  a  soft  and  fungus-like  mass  of  flesh,  rather  like  the 
substance  of  the  spleen,  which  adheres  to  the  surface  of  the  uterus 
and  transmits  to  the  foetus  in  proportion  as  it  grows  the  nourishment 
for  it  which  reaches  the  uterus  in  the  form  of  blood  and  spirits". 
Then,  going  on  to  discuss  the  functions  of  the  jecor  uterinae,  as 
he  calls  the  placenta  (with  what  justice  may  be  seen  by  turning  to 
Section  8-5),  he  devotes  a  chapter  to  De  vasorum  umbilicalium  origine, 
and,  contradicting  Hippocrates,  Galen,  Erasistratus,  and  Aetius,  says 
that  the  maternal  and  foetal  blood-vessels  do  not  pass  into  each 
other  by  a  free  passage.  "This  is  repugnant  to  sense",  he  writes, 
"and  as  may  be  seen  by  ocular  inspection,  these  vessels  do  not  reach 
the  inner  membrane  of  the  uterus,  for  the  substance  of  the  placenta 
is  placed  between  their  ramifications  and  the  proper  substance  of 
the  womb."  He  was  thus  the  first  to  maintain  that  the  maternal 
and  foetal  circulations  are  separate,  but  he  naturally  did  not,  and 
could  not,  speak  of  circulations,  since  he  lived  before  Harvey.  Nor 
could  he  have  satisfactorily  proved  his  point  with  the  means  then 
at  his  command,  and,  as  we  shall  see,  it  was  to  take  another  century 
before  the  proof  was  given.  Apart  from  this  valuable  contribution 
to  embryology,  Arantius  gave  some  admirable  anatomical  descrip- 
tions of  the  foetal  membranes. 

Hieronymus  Fabricius  ab  Aquapendente,  the  pupil  of  Fallopius, 
has  always  been  given  an  important  place  in  the  history  of  embryo- 
logy by  those  who  have  written  on  him.  As  one  comes  upon  him 
in  the  process  of  tracing  out  that  history  itself,  however,  he  does 
not  take  such  a  high  place.  With  the  statement,  for  instance,  that 
"Fabricius  carried  embryology  far  beyond  where  Goiter  had  left 
it  and  elevated  it  at  one  bound  into  an  independent  science"  I 
find  that  I  cannot  agree.  Embryologists  who  called  themselves 
that  and  nothing  else  did  not  appear  till  the  end  of  the  eighteenth 
century,  and  it  seems  to  me  doubtful  whether  the  anatomical  ad- 
vances in  embryology  made  by  Fabricius  are  not  counterbalanced 
by  the  erroneous  theories  which  he  invented  at  the  same  time.  His 
De  Formatione  Ovi  et  Pulli  pennatorum,  and  his  De  Formato  Foetu  of  1604 
show  far  more  scholasticism  and  mere  argumentativeness  than  is  to 
be  found  in  Goiter,  and  are  remarkable  for  their  bulk.  Fabricius 
seems  to  have  had  a  genius  for  exsuccous  and  formal  discussions.  He 
spends  much  time,  for  example,  in  taking  up  the  problem  of  whether 


ii6  EMBRYOLOGY   FROM   GALEN  [pt.  ii 

the  yolk  of  the  hen's  egg  is  more  earthy  than  the  white,  and  looking 
at  it  from  all  possible  angles.  He  disagrees  at  last  with  Aristotle 
and  decides  that  the  white  is  the  more  earthy.  Bones,  he  says,  are 
white,  but  also  very  earthy.  The  albumen  is  colder,  stickier,  and 
heavier  than  the  yolk,  "sequitur,  terrestrius  esse^\  And  this  particular 
example  is  the  more  flagrant  because  the  actual  matter  of  it  is 
fundamentally  physico-chemical.  But,  in  addition,  he  introduced  a 
number  of  grave  errors  and  misleading  theories  into  embryology,  so 
that  subsequently  Harvey  had  to  spend  a  large  part  of  his  time 
refuting  them.  Fabricius  was,  indeed,  a  good  comparative  anatomist, 
and  it  is  upon  that  ground  that  he  deserves  praise:  his  plates,  some 
of  which  are  reproduced  herewith,  were  far  better  than  anything 
before  and  for  a  long  time  afterwards.  He  dissected  embryos  of  man, 
rabbit,  guinea-pig,  mouse,  dog,  cat,  sheep,  pig,  horse,  ox,  goat,  deer, 
dogfish,  and  viper,  a  comparative  study  which  had  certainly  never 
been  made  previously. 

In  his  first  tractate  he  begins  by  dealing  with  a  question  not  unlike 
that  of  how  the  sardines  got  into  the  tin,  i.e.  how  the  contents  got 
into  the  hard-shelled  egg.  He  rejects  Aristotle's  idea  that  the  egg 
is  formed  in  the  oviduct  by  a  kind  of  umbilicus,  and  ascribes  its 
growth  there  to  transudation  through  the  blood-vessels.  He  marks 
a  definite  advance  upon  Aristotle  when  he  says  that  silkworms  and 
other  insects  are  born  into  their  larval  state  from  an  egg,  though  he 
still  terms  the  chrysalis  an  egg,  and  therefore  holds  that  they  are 
generated  twice.  Then  follows  his  discussion  of  what  part  of  the  egg 
the  chick  comes  from.  The  chalazae,  he  says,  are  not  semen,  for  the 
semen  is  not  present  at  all  in  the  fertilised  egg.  His  argument  sounds 
peculiar  when  he  says  that  both  the  white  and  yolk  of  the  egg  are 
the  food  of  the  embryo,  for  neither  of  them  is  absent  at  the  end  of 
incubation,  therefore  neither  of  them  is  its  material.  Hippocrates 
had  said,  "^ex  luteo  gigni,  ex  albo  nutriri'';  Aristotle  had  said,  "ex 
albo  fieri,  ex  luteo  nutrirV\  The  latter  was  the  view  generally  held 
in  the  sixteenth  century,  as  may  be  gathered  from  Ambrosius 
Calepinus'  dictionary,  Scaliger's  Commentary  on  Aristotle,  and  the 
treatise  on  the  soul  of  Johannes  Grammaticus. 

Fabricius  now  says  both  nourish,  neither  makes.  This  distinction 
between  food  and  building-materials  seems  to  us  unnecessary,  but 
it  had  a  great  influence  on  later  thought.  Fabricius  devotes  much 
time  to  proving,  as  he  thinks,  that  albumen  and  white  are  of  the 




same  nature,  and  adduces  the  fact  that  "in  cooking  the  white  hardens 
first,  whether  the  egg  be  boiled  or  poached,  but  the  yolk  hardens 
also  if  the  heat  is  more",  comparing  the  heat  of  the  kitchen  to  the 
innate  heat  of  the  chick.  "But  you  will  say",  he  goes  on,  "if  the 
albumen  and  the  yolk  are  the  food  of  the  chick  in  the  egg,  what 
then  must  we  decide  the  material  of  the  chick  to  be,  since  we  have 
already  said  that  the  semen  is  not  present  in  the  eggs.  You  will 
find  this  material  from  an  enumeration  of  the  parts  of  the  egg — there 
remains  only  the  shell,  the  two  membranes,  and  the  chalazae; — 
nobody  will  assign  the  membranes  or  the  shell  as  the  material  of 
the  chick,  therefore  the  chalazae  alone  are  the  fitting  substance  out 
of  which  it  can  be  made."  Having  discovered  this  truth  by  the 
infallible  processes  of  logic,  Fabricius  brings  all  kinds  of  arguments 
forward  to  support  it;  he  adduces  the  three  nodes  in  the  chalazae 
as  the  precursors  of  brain,  heart,  and  liver;  tadpoles,  he  thinks, 
resemble  significantly  the  chalazae,  being  "armless  legless  spines". 
The  eyes  are  transparent,  so  are  the  chalazae,  therefore  the  latter 
must  give  rise  to  the  former.  The  liver  is  formed  as  soon  as  the  heart 
but  is  practically  invisible  as  it  does  not  palpitate.  One  of  his  most 
gratuitous  errors  was  the  suggestion,  now  newly  introduced,  that  the 
heart  (and  other  organs)  of  the  foetus  has  no  proper  function,  no 
munus  publicum,  but  beats  only  in  order  to  preserve  its  own  life. 
Then  there  is  a  considerable  section  called  De  Ovorum  utilitatibus, 
which  almost  does  for  the  hen's  egg  what  Galen's  De  Usu  Partium 
did  for  the  human  body,  and  in  which  such  questions  as  Why 
the  shell  is  hard  and  porous?  and  Why  there  are  any  membranes 
in  the  egg?  are  taken  up  and  answered  with  an  elaborate  display 
of  common  sense.  The  influence  of  Galen  is  perceptible  in  a  passage 
about  a  liver-like  substance  being  formed  if  blood  is  freshly  shed  into 
hot  water,  in  the  usual  terminology  of  formative  faculties,  and  in  the 
division  of  fleshes  into  white  and  red,  though  the  former  is  not 
specifically  derived  fi"om  the  semen  nor  the  latter  from  the  menstrual 
blood.  The  human  placenta  is  described  as  cotyledonous,  and  need- 
less confusion  is  caused  by  the  doctrine  that  the  "liquors,  humours, 
or  rather,  excrements,  around  the  foetus,  are  two  in  number,  sweat 
and  urine,  the  former  in  the  amnios,  the  latter  in  the  allantois". 
But  the  drawings  and  illustrations  of  Fabricius'  work  are  beautiful 
and  accurate — so  much  so,  indeed,  that  it  will  always  remain 
a    mystery    how    the    man    who    figured    the    early   stages   of  the 

ii8  FROM   GALEN  TO  THE  RENAISSANCE        [pt.  ii 

development  of  the  chick  as  Fabricius  did,  showing  the  blood- 
vessels radiating  from  the  minute  heart,  should  have  been  able 
to  propound  the  thesis  that  the  chalazae  were  the  material  of  the 

The  other  biologist  to  whom  Harvey  was  most  indebted  was 
Andreas  Laurentius  of  Montpellier,  whose  Historia  Anatomica  (printed 
with  his  other  works  in  1628)  contained  a  whole  book  (viii)  devoted 
to  embryology,  but  which  presents  us  with  nothing  except  a  com- 
mentary on  Hippocrates  and  Aristotle.  The  only  evidences  of  life 
are  furnished  by  two  polemics,  one  of  which  was  against  Simon 
Petreus  of  Paris,  who  had  propounded  some  new  views  about  the 
foetal  circulation.  Laurentius  gave  also  a  table  showing  the  changes 
which  occur  in  the  heart  and  lungs  of  the  foetus  at  birth. 

It  was  about  this  time  that  the  embryological  observations  of  that 
many-sided  genius,  Hieronymus  Cardanus,  began  to  attract  atten- 
tion. His  main  thesis  was  that  the  limbs  of  the  embryo  were  alone 
derived  from  the  yolk,  while  the  rest  of  the  body  came  from  the 
white.  This  was  a  well-meant  attempt  to  mediate  between  the  two 
traditions  headed  respectively  by  Aristotle  and  Hippocrates,  but  the 
arguments  in  support  of  it  were  not  even  remarkable  for  ingenuity. 
Constantinus  Varolius  treated  of  the  formation  of  the  embryo  in  a 
book  which  appeared  in  1591,  but  very  inadequately.  He  had 
certainly  opened  hen's  eggs,  and  describes  the  fourth-day  embryo 
as  forma  minimi  faseoli.  But  nearly  every  one  of  his  marginal 
headings  begins  with  the  word  Cur,  and  this  tells  its  own  story, 
for  the  didactic  style  rarely  hides  genuine  works  of  research.  Johannes 
Fernelius,  a  rather  earlier  worker,  in  his  De  Hominis  Procreatione  fol- 
lowed Aristotle  and  Galen  in  nearly  all  particulars,  and  made  no 
real  contribution  to  embryology.  On  its  practical  obstetrical  side, 
the  sixteenth  century  produced  some  remarkable  compilations  of 
ancient  gynaecological  writings.  The  first  of  these  was  that  of  Caspar 
Wolf,  which  was  published  at  Ziirich  in  1566,  and,  after  having 
been  enlarged  by  Caspar  Bauhin  in  1586,  subsequently  formed  the 
backbone  of  the  most  important  and  famous  one,  namely,  that  of 
Israel  Spach  (Strassburg,  1597).  Although  these  composite  text- 
books represented  no  real  embryological  progress,  they  yet  showed 
that  great  interest  in  development  was  alive,  an  interest  which, 
though  doubtless  utilitarian  in  its  origin,  could  hardly  fail  to  lead 
to  advances  of  a  theoretical  nature.    (See  Fig.  5.) 

Fig.  5.   Illustration  from  W.  H.  Ryff's  Anatomia  of  1541. 

120  FROM   GALEN  TO  THE  RENAISSANCE        [pt.  ii 

The  obstetrical  literature  intended  for  midwives  is  also  of  great 
interest.  It  was  about  this  time  that  the  first  popular  guides  to  their 
subject  began  to  appear,  founded  not  upon  mere  superstition  and 
the  remnants  of  ancient  knowledge  derived  in  roundabout  fashion 
through  Syriac  and  Arabic,  but  either  upon  a  careful  study  of  Galen 
and  Aristotle,  or  upon  the  results  of  dissections  and  living  speculation. 
The  principal  representative  of  the  former  class  is  that  of  Jacob 
Rueff,  which  appeared  in  1554  and  was  called  De  Conceptu  et  Genera- 
tione  Hominis.  Although  written  in  Latin,  it  was  evidently  a  popular 
work,  for  the  illustrations  given  in  it  are  such  as  would  naturally 
be  incorporated  in  such  a  book.  It  is  the  illustrations  which  give  it 
its  importance,  and  I  reproduce  them  in  Fig.  6.  I  think  they  show 
very  clearly  what  the  general  ideas  were  at  this  period  about  mam- 
malian embryology,  and  thus  afford  us  a  precious  insight  into  what 
was  in  the  minds  of  such  writers  as  Riolanus  the  elder,  Mercurialis, 
Saxonia,  Rondeletius,  Venusti,  Holler  and  Vallesius.  There  are  many 
points  which  their  expositions  of  foetal  growth  and  development  leave 
vague,  and  without  Rueff  it  would  be  difficult  or  impossible  to  picture 
in  what  manner  they  imagined  it  to  go  on.  Rueff 's  text  follows  Galen 
and  Aristotle  with  fidelity,  as  does  theirs — with  the  exception  of  a  few 
minor  ideas  not  quite  consonant  with  this. 

In  (a)  of  Fig.  6  Rueff  portrays  the  mixture  of  semen  and  menstrual 
blood  in  the  womb,  or,  as  he  loosely  refers  to  it,  of  both  seeds, 
coagulating  into  a  pink  egg-shaped  mass  surrounded  with  a  fine 
pellicle,  {b)  shows  the  same  mass  in  the  uterus  and  wrapped  round 
with  the  three  coats,  amnion,  chorion,  and  allantois — a  lamentable 
but  interesting  misrepresentation  of  the  facts.  Then  in  {c)  it  is  shown 
that  upon  the  surface  of  the  yolk-like  mass  of  semen  and  blood 
appear  "three  tiny  white  points  not  unlike  coagulated  milk",  these 
being  the  first  origins  of  the  liver,  the  heart,  and  the  brain.  Next  {d) 
shows  the  first  blood-vessels  springing  from  the  heart,  four  in  number, 
and  distributing  themselves  over  the  surface  of  the  mass.  It  is  plain 
that  Rueff  must  either  have  opened  hen's  eggs  himself  and  seen  the 
early  growth  of  the  blastoderm  or  have  been  told  about  it  by  some 
observer  such  as  Goiter  or  Aldrovandus.  He  could  not  have  copied 
his  pseudo-blastoderm  pictures  from  their  works,  for  in  1554  none 
of  them  had  appeared,  and,  as  far  as  I  know,  there  were  no  similar 
illustrations  in  existence  at  that  time. 

After  this  point  the  pictures  grow  even  more  fanciful,  and,  in  (^), 

Fig.  6.    Illustrations  from  Jacob  Rueff's  De  Conceptu  et  Generatione  Hominis  of  1554 
(arranged  by  Singer)  showing  the  Aristotelian  coagulum  of  blood  and  seed  in  the  uterus. 

122  EMBRYOLOGY   FROM  GALEN  [pt.  ii 

the  first  outline  of  the  cranium  is  seen  taking  shape  in  the  upper 
part  of  the  "egg".  In  (/)  the  blood-vessels  have  suddenly  assumed 
the  outline  of  a  human  being,  and  in  (g)  the  finished  product  is  seen. 
Rueff  gives  what  seems  to  be  a  mnemonic  in  hexameters : 

iniectum  semen,  sex  primis  certe  diebus 
est  quasi  lac :  reliquisque  novem  sit  sanguis ;  at  inde 
consolidat  duodena  dies;  bis  nona  deinceps 
effigiat;  tempusque  sequens  producit  ad  ortum 
talis  enim  praedicto  tempore  figura  consit. 

Rueff  gives  some  excellent  diagrams  of  the  foetus  in  utero  with 
relation  to  the  rest  of  the  body,  and  the  various  positions  which  are 
familiar  to  obstetricians.  His  teratology  is  less  happy,  for  he  attri- 
butes the  production  of  monsters  to  the  direct  action  of  God,  though 
he  does  venture  upon  a  few  speculations  concerning  "corrupt  seed". 
But  his  principal  significance  for  this  history  is  that,  in  his  picture 
of  the  yolk-like  mass  of  mixed  semen  and  blood  and  the  pseudo- 
blastoderm  upon  it,  he  throws  a  good  light  on  the  conceptions  of 
the  time. 

Rueff 's  book  was  subsequently  translated  into  English,  and  had 
many  editions  as  The  Expert  Midwife. 

The  principal  representative  of  the  second  class  of  popular  books 
of  this  period  is  that  of  Euch.  Rhodion,  or  Rosslein,  which  was 
translated  into  English,  and  published  as  his  own  work,  by  Thomas 
Raynold,  "  physition  ",  in  1 545,  under  the  title  of  The  Byrth  ofMankynde 
otherwyse  named  The  Woman" s  Book  (cf.  d'Arcy  Power).  It  was  the  first 
book  in  the  English  language  to  contain  copper  engravings.  They 
were  variants  of  the  traditional  Soranus-Moschion  figures.  The 
Rosslein-Raynold  book  pays  less  attention  to  Galenic  theory  than  does 
that  of  Rueff,  and  includes  much  better  drawings  of  actual  dissec- 
tions. Another  famous  obstetrical  book  was  that  of  Scipio  Mercurius; 
for  further  information  here  see  Spencer. 

The  minor  embryologists  of  the  sixteenth  century  included  among 
them  Ambroise  Pare,  the  founder  of  modern  surgery.  His  teaching 
on  generation  involved  nothing  original,  but  it  seems  to  have  been 
Galenism  interpreted  by  a  very  intelligent  and  well-balanced,  un- 
speculative  mind.  The  three-bubble  theory  appears  in  him  very 
clearly;  thus,  we  read,  "The  seed  boileth  and  fermenteth  in  the 
womb,  and  swelleth  into  three  bubbles  or  bladders" — the  brain,  the 


liver,  and  the  heart.  Fare's  illustrations  are  copied  wholesale  from 
Vesalius  and  Rueff,  without  acknowledgment.  The  last  author  to 
take  the  three-bubble  theory  quite  seriously  was  A.  Deusingius,  who 
wrote  in  1665,  after  Harvey.  Others  who  deserve  a  mention,  but 
no  more,  were  Severinus  Pinaeus,  L.  Bonaciolus  and  Felix  Platter. 
None  of  them  made  any  advance,  and  the  illustrations  of  the  former's 
De  Virginitatibus  notis  graviditate  et  partu  were  almost  ludicrous. 

Hieronymus  Capivaccius,  F.  Licetus,  J.  Costaeus  and  V.  Cardelinus, 
who  wrote  in  1608,  were  the  last  true  supporters  of  the  ancient 
theories,  such  as  that  the  male  embryo  was  twice  as  hot  and  developed 
twice  as  quickly  as  the  female. 



3-1.    The  Opening  Years  of  the  Seventeenth  Century 

iEmilius  Parisanus,  a  Venetian,  now  dealt  with  embryology  in  the 
fourth,  fifth,  and  sixth  books  of  his  De  Subtilitate.  They  were  entitled 
as  follows:  "(4)  Of  the  principles  and  first  instruments  of  the  soul 
and  of  innate  heat,  (5)  Of  the  material  of  the  embryo  and  of  its 
efficient  cause,  (6)  Of  the  part  of  the  animal  body  which  is  first 
made,  and  of  the  mode  and  order  of  procreation".  Parisanus  is 
very  wordy,  but  he  has  the  merit  of  giving  many  quotations  from 
the  lesser  known  authors,  and  providing  (as  a  rule)  accurate  refer- 
ences. He  held  that  the  spleen  was  formed  in  all  development  before 
the  heart,  and  that  neither  heart  nor  lungs  moved  in  utero.  With 
regard  to  the  controversy  over  the  function  of  white  and  yolk,  he 
was  in  agreement  with  Fabricius,  but  he  firmly  opposed  the  view 
that  the  chalazae  were  the  first  material  of  the  chick,  as  much,  it 
must  be  confessed,  because  of  the  opinion  of  Aristotle  as  from  his 
own  observation.  Nevertheless,  his  own  observations  were  note- 
worthy, and  he  will  always  be  remembered  for  his  discovery  of  the 
fact  that  the  heart  of  the  chick  begins  to  beat  some  time  before  any 
red  blood  appears  in  it. 

Parisanus  was  the  last  of  the  macro-iconographic  group  of  sixteenth- 
century  embryologists.  Their  labours  established  the  fundamental 
morphological  facts  about  the  developing  embryo;  the  first  great 
step  in  the  history  of  embryology.  But  there  were  numerous  errors 
in  their  work,  and  Harvey,  who  occupies  a  terminal  or  boundary 
position,  was  destined  to  correct  them.  He  marks  the  transition  from 
the  static  to  the  dynamic  conception  of  embryology,  from  the  study 
of  the  embryo  as  a  changing  succession  of  shapes,  to  the  study  of  it 
as  a  causally  governed  organisation  of  an  initial  physical  complexity, 
in  a  word,  from  Goiter  and  Fabricius  to  Descartes  and  Mayow. 
Iconography  did  not  die :  on  the  contrary,  the  improvement  of  the 
microscope  gave  it  new  life,  and  the  micro-iconographic  school 
emerged  with  its  principal  glory,  Malpighi. 


Harvey  sums  up  the  work  of  the  macro-iconographic  period  in  the 
historical  introduction  contained  in  Ex.  xiv  of  his  De  Generatione 
Animalium.  I  give  it  in  full  in  the  beautiful  seventeenth  century 
English  into  which  Harvey's  Latin  was  translated  under  his  guidance 
by  the  physician,  Martin  Llewellyn, 

"We  have  already  discovered  the  Formation,  and  Generation  of 
the  Egge;  it  remains  that  we  now  deliver  our  Observations,  con- 
cerning the  Procreation  of  the  Chicken  out  of  the  Egge.  An  under- 
taking equally  difficult,  usefull,  and  pleasant  as  the  former.  For 
Nature's  Rudiments  and  Attempts  are  involved  in  obscurity  and 
deep  night,  and  so  perplext  with  subtilties,  that  they  delude  the  most 
piercing  wit,  as  well  as  the  sharpest  eye.  Nor  can  we  easier  discover 
the  secret  recesses,  and  dark  principles  of  Generation  than  the  method 
of  the  fabrick  and  composure  of  the  whole  world.  In  this  reciprocal 
interchange  of  Generation  and  Corruption  consists  the  ^Eternity 
and  Duration  of  mortal  creatures.  And  as  the  Rising  and  Setting 
of  the  Sun,  doth  by  continued  revolutions  complete  and  perfect 
Time;  so  doth  the  alternative  vicissitude  of  Individuums,  by  a 
constant  repetition  of  the  same  species,  perpetuate  the  continuance 
of  fading  things. 

"Those  Authors  which  have  delivered  any  thing  touching  this 
subject,  do  for  the  most  part  tread  a  several  path,  for  having  their 
Judgements  prepossessed  with  their  own  private  opinions,  they  pro- 
ceed to  erect  and  fashion  principles  proportionable  to  them. 

"Aristotle  of  old,  and  Hieronymus  Fabricius  of  late,  have  written 
so  accurately  concerning  the  Formation  and  Generation  of  the  Foetus 
out  of  the  Egge,  that  they  seem  to  have  left  little  to  the  industry 
of  Posterity,  And  yet  Ulysses  Aldrovandus  hath  undertaken  the 
description  of  the  Pullulation  or  Formation  of  the  chicken  out  of  the 
Egge,  out  of  his  own  Observations ;  wherein  he  seems  rather  to  have 
directed  and  guided  his  thoughts  by  the  Authority  of  Aristotle,  than 
by  his  own  experience. 

"For  Volcherus  Goiter,  living  at  Bononia  at  the  same  time  did 
by  the  advice  of  the  said  Aldrovandus  (whom  he  calls  Tutor)  dayly 
employ  himself  in  the  opening  of  Egges  sat  upon  by  the  Hen,  and 
hath  discovered  many  things  truer  than  Aldrovandus  himself,  of 
which  he  also  could  not  be  ignorant.  Likewise  iEmilius  Parisanus 
(a  Venetian  Doctor)  despising  other  mens  opinions  hath  fancied  A 
new  procreation  of  the  Chicken  out  of  the  Egge. 

126  EMBRYOLOGY   IN    THE   SEVENTEENTH      [pt.  ii 

"But  because  somethings,  (according  to  our  experience)  and  those 
of  great  moment  and  consequence,  are  much  otherwise  than  hath 
been  yet  delivered,  I  shall  declare  to  you  what  dayly  progress  is  made 
in  the  egge,  and  what  parts  are  altered,  especially  about  the  first 
dayes  of  Incubation;  at  which  time  all  things  are  most  intricate, 
confused,  and  hard  to  observe,  and  about  which  authors  do  chiefly 
stickle  for  their  own  observations,  which  they  accomodate  rather  to 
their  own  preconceived  perswasions  (which  they  have  entertained 
concerning  the  Material  and  Efficient  Causes  of  the  generation  of 
Animals)  than  to  truth  herself. 

"Aldrovandus,  partaking  of  the  same  error  with  Aristotle,  saith 
(which  none  but  a  blind  man  can  subscribe  to)  that  the  Yolk  doth 
in  the  first  dayes,  arise  to  the  Acute  Angle  of  the  Egge ;  and  thinks 
the  Grandines  to  be  the  Seed  of  the  Cock;  and  that  the  Pullus  is 
framed  out  of  them,  but  nourished  as  well  by  the  yolk  as  the  white ; 
which  is  clean  contrary  to  Aristotle's  opinion,  who  conceived  the 
Grandines  to  conduce  nothing  to  the  fecundity  of  the  egge.  Volcherus 
Goiter  delivers  truer  things,  and  more  consonant  to  Autopsie,  yet  his 
three  Globuli  are  meer  fables.  Nor  did  he  rightly  consider  the 
principle  from  whence  the  Foetus  is  derived  in  the  Egg.  Hieronymus 
Fabricius  indeed  contends,  that  the  Grandines  are  not  the  seed  of 
the  cock,  and  yet  he  will  have  the  body  of  the  Chicken  to  be  framed 
out  of  them  (as  out  of  its  first  matter)  being  made  fruitful  by  the  seed 
of  the  cock.  He  likewise  saw  the  Original  of  the  Chicken  in  the  Egge; 
namely  the  Macula,  or  Cicatricula  annexed  to  the  membrane  of  the 
Yolke  but  conceived  it  to  be  onely  a  Relique  of  the  stalk  broken  off, 
and  an  in-firmity  of  blemish  onely  of  the  Egge,  and  not  a  principle 
part  of  it.  Parisanus  hath  plentifully  confuted  Fabricius  his  opinion 
concerning  the  Chalazae  or  Grandines,  and  yet  himself  is  evidently 
at  a  loss  in  some  certaine  circles  and  points  of  the  Principle  parts 
of  the  Foetus  (namely  the  Liver  and  the  Heart)  and  seems  to  have 
observed  a  Principium  or  first  Principle  of  the  Foetus,  but  not  to 
have  known  which  it  was,  in  that  he  saith,  that  the  Punctum  Album 
in  the  Middle  of  the  Circles  is  the  Cocks  Seed  out  of  which  the  Chicken 
is  made.  So  that  it  comes  to  pass  that  while  each  of  them  desire  to 
reduce  the  manner  of  the  Formation  of  the  Chicken  out  of  the  Egge 
to  their  own  opinions  they  are  all  wide  from  the  mark." 

Before  discussing  how  Harvey  put  them  right,  however,  there  are 
a  number  of  other  matters  to  be  mentioned.    Parisanus'  work  was 


published  in  1623,  and  twenty-five  years  were  to  elapse  before 
Harvey's  Exercitations  were  to  be  put  before  the  learned  world  by 
George  Ent.  In  that  time  not  a  few  events  of  importance  for  the 
history  of  embryology  took  place. 

It  will  be  convenient  to  speak  first  of  Adrianus  Spigelius,  whose 
De  Formato  Foetu  appeared  in  1 63 1 .  In  this  book  the  plates  of  the 
gravid  uterus  which  had  been  prepared  some  years  before  for  Julius 
Casserius  were  now  published.  They  had  more  influence  than 
Spigelius'  text,  perhaps,  in  contributing  to  the  permanent  fame  of 
his  book. 

He  gives  for  the  most  part  straightforward  anatomical  descriptions, 
but  he  returns  to  the  notion  of  a  cotyledonous  placenta  in  man,  and 
he  combats  Arantius'  opinions  about  the  placenta.  Arantius  had  said 
that  the  function  of  the  jecor  uterinae  was  to  purify  the  blood- 
supply  to  the  foetus,  a  thoroughly  modern  idea,  but  Spigelius  opposes 
this  on  two  grounds,  firstly,  because  the  foetus  has  its  own  organs 
for  purifying  blood,  and  secondly,  because,  if  Arantius  was  right, 
the  placenta  would  always  be  as  red  as  blood,  but  this  is  not  the  case 
in  such  animals  as  the  sheep.  Spigelius  himself  thought  that  the 
placenta  was  for  the  purpose  of  preventing  severe  loss  of  blood  at 
birth,  as  would  be  the  case  if  the  embryo  was  joined  to  the  mother 
with  only  one  big  vessel  and  not  a  great  many  little  ones. 

However,  Spigelius  upholds  the  view,  taken  by  Rufus  of  Ephesus 
and  by  Vesalius,  that  the  allantois  contains  the  foetal  urine,  which 
has  to  be  separated  from  the  amniotic  liquid  in  which  the  embryo 
is,  because  it  would  corrode  the  embryonic  skin  [ne  cuti  tenellae 
aliquod  damnum  urinae  acrimonia  inferret).  This  passage  is  interesting, 
as  showing  biochemical  rudiments.  The  first  discussion  of  the 
vernix  caseosa,  or  sordes,  as  he  calls  it,  appears  in  Spigelius,  who, 
however,  hazards  no  guess  as  to  its  nature.  He  is  happy  in  his 
refutation  of  Laurentius,  who  had  affirmed  that  the  foetal  heart  did 
not  beat  in  utero,  and  he  shows  some  advance  on  all  previous  writers 
save  Arantius  in  declaring  that  the  umbilical  vessels  take  vital  spirits 
away  from  the  foetal  heart,  not  exclusively  to  it.  He  gave,  moreover, 
the  first  denial  of  the  presence  of  a  nerve  in  the  umbilical  cord,  and  also 
made  the  first  observation  of  the  occurrence  of  milk  in  foetal  breasts 
at  birth  (for  the  endocrinological  explanation  of  this  see  Section  15). 
Finally,  he  abolished  at  last  the  notion  that  the  meconium  in  the 
foetal  intestines  argued  eating  in  utero  on  the  part  of  the  embryo. 

128  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

Riolanus  the  younger,  the  correspondent  and  almost  exactly  the 
contemporary  of  Harvey,  was  Professor  in  Paris  and  published  his 
Anthropographia  in  1618.  As  he  was  a  keen  advocate  of  the  ancient 
views,  his  section  on  the  formation  of  the  foetus  has  little  importance. 
Yet  it  contains  the  first  known  instance  of  the  use  of  the  lens  in  embryo- 
logy, the  germ  of  that  powerful  instrument  which  was  to  lead  in 
due  course  to  so  many  discoveries.  "In  aborted  embryos",  said 
Riolanus,  "the  structure  is  damaged  and  can  often  not  be  properly 
seen,  even  when  you  make  use  of  lenses  [conspicilid]  which  make 
objects  so  much  bigger  and  more  complicated  than  they  ordinarily 

The  De  Formatrice  Foetus  of  Thomas  Fienus,  Professor  at  Louvain 
and  a  friend  of  Gassendi,  published  in  1620,  is  interesting  because 
it  is  the  middle  term  between  Aristotle  and  Driesch.  As  the  title- 
page  informs  us,  he  sets  out  to  demonstrate  that  the  rational  soul  is 
infused  into  the  human  embryo  on  the  third  day  after  conception. 
This  by  itself  would  not  be  very  attractive,  but  the  most  cursory 
inspection  shows  that  Fienus'  interests  were  not  at  all  theological. 
He  divides  the  book  up  into  seven  main  questions,  (i)  What  is  the 
efficient  cause  of  embryogeny?  He  concludes  that  it  is  neither  God, 
nor  Intelligence,  nor  anima  mundi  (influence  of  Neo-platonism  here 
as  on  Galileo).  (2)  Is  it  in  the  uterus  or  in  the  seed?  In  the  latter, 
says  Fienus,  adding  a  list  of  authorities  who  agree  with  this  view — 
Haly-Abbas,  Gaietanus,  Zonzinas,  Turisanus,  Fernelius,  Vallesius, 
Peramatus,  Saxonia,  Carrerius,  Zegarra,  Mercurialis,  Massaria,  and 
Archangelus,  ^' solus  Fabio  Pacio  utero  imprudenter  adscribit''  (!).  (3)  Is 
it  heat?  Fienus  nearly  decided  that  it  was,  and,  if  he  had  done 
so,  would  have  shown  a  modern  mind,  but  no,  he  gave  his 
opinion  against  it,  saying,  "the  process  (of  development)  is  so  divine 
and  wonderful  that  it  would  be  ridiculous  to  ascribe  it  to  heat,  a 
mere  naked  and  simple  quality".  After  weighing  various  other 
alternatives  in  questions  (4),  (5)  and  (6),  he  asks  whether  it  is 
^'^ anima  seminis  post  conceptum  adveniens''  (7),  and  concludes  that  it  is. 
It  is  here  that  he  becomes  really  interesting,  for  he  quotes  with 
approval  certain  writers,  e.g.  Alexander  Aphrodisias  [Organicum  corpus 
esse  organicum  ab  anima  et  anima  praeexistere  organizationi) ,  Themistius 
{Anima  fabricatur  architecturaque  sibi  domicilium  et  accommodatum  instru- 
mentum)  and  Marsilio  Ficino  in  his  commentary  on  Plato's  Timaeus 
[Priusquam  adultum  sit  corpus,  anima  tota  in  illius  fabrica  occupatur),  and 


then  maintains  with  them  that  the  soul  is  the  principle  which 
organises  the  body  from  within,  arranging  an  organ  for  each  of 
its  faculties  and  preparing  a  residence  for  itself,  not  merely  allowing 
itself  to  be  breathed  into  a  being  which  has  already  organised 
itself  "The  conformation  of  the  foetus  is  a  vital,  not  a  natural, 
action",  he  says.  He  develops  this  idea  in  the  remainder  of  the 
book;  according  to  him,  the  seed  first  coagulates  the  menstrual 
blood  into  an  amorphous  cake,  taking  three  days  to  do  so,  after 
which,  the  rational  (not  vegetative  or  sensitive)  soul  (entelechy), 
which  has  entered  the  uterus  with  the  seed,  finding  a  suitable 
mass  of  shapeless  material,  enters  into  it  and  begins  to  give  it  a 
shape.  Fienus  was  attacked  by  several  writers,  and  published  a 
defence  of  his  views. 

Later  writers  on  the  same  subject  included  Fidelis,  Teichmeyer, 
Albertus,  de  Reies,  Torreblanca  and  de  Mendoza.  The  Spanish 
influence  here  is  perhaps  significant.  Hieronymus  Florentinus,  who 
adopted  the  same  standpoint  as  Fienus  in  1658  was  forced  to  recant  it. 

In  1625  Joseph  de  Aromatari,  a  Venetian,  included  in  his  epistle 
on  plants  the  first  definite  statement  of  the  preformationist  theory 
since  Seneca,  but  he  did  not  develop  the  idea.  He  had  noted  that 
in  bulbs  and  some  seeds  the  rudiments  of  many  parts  of  the  adult 
plant  can  be  seen  even  without  glass  or  microscope,  and  this  led  him 
to  suggest  that  probably  in  all  animals  as  well  as  plants  a  similar 
thing  was  true.  "And  as  for  the  eggs  of  fowls",  he  said,  "I  think  the 
embryo  is  already  roughly  sketched  out  in  the  egg  before  being  formed 
at  all  by  the  hen  [quod  attinet  ad  ova  gallinarum,  existimamus  quidem 
pullum  in  ovo  delineatum  esse,  antequam  formatur  a  gallina].''  This  sug- 
gestion did  not  begin  to  bear  its  malignant  fruits  till  the  time  of 
Swammerdam  and  Malpighi. 

Johannes  Sinibaldi's  Geneanthropia  might  be  mentioned  as  belonging 
to  this  time.  It  was  a  compilation  of  facts  relating  to  the  generation 
of  man,  but  it  expressly  excluded  from  its  field  any  discussion  of  the 
embryo.  It  is  no  more  important  for  our  subject  than  the  queer 
Ovi  Encomium  of  Erycius  Puteanus,  another  of  Gassendi's  friends,  which 
has  already  been  referred  to  (p.  8). 

3-2.    Kenelm  Digby  and  Nathaniel  Highmore 

Much  more  significant  was  the  controversy  between  Sir  Kenelm 
Digby  and  Nathaniel  Highmore.    In  1644,  Sir  Kenelm,  whose  in- 

I30  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

triguing  personality  will  be  sufficiently  familiar  to  anyone  even  slightly 
acquainted  with  seventeenth-century  England,  and  whose  biographic 
details  may  be  found  in  John  Aubrey,  published  a  work  with  the 
following  title:  Two  treatises,  in  the  one  of  which,  The  Nature  of  Bodies, 
in  the  other,  The  Nature  of  Man's  Soule  is  looked  into,  in  way  of  discovery 
of  the  Immortality  of  Reasonable  Soules.  It  was  inscribed  in  a  charming 
dedication  to  his  son,  and  consisted,  in  brief,  of  a  survey  of  the  whole 
realms  of  metaphysics,  physics,  and  biology  from  a  very  individual 
point  of  view. 

One  of  Sir  Kenelm's  principal  objects  in  writing  was  apparently 
to  attack  the  old  terminology  of "  qualities "  in  physics  and  "faculties  " 
in  biology.  To  say,  as  contemporary  reasoning  did,  that  bodies  were 
red  or  blue  because  they  possessed  a  quality  of  redness  or  blueness 
which  caused  them  to  appear  red  or  blue  to  us,  or  again,  to  say  that 
the  heart  beat  because  it  was  informed  by  a  sphygmic  faculty,  or, 
to  take  the  famous  example,  that  opium  sent  people  to  sleep  because 
it  contained  in  it  a  dormitive  virtue,  appeared  mere  nonsense  and 
word-spinning  to  Digby,  "the  last  refuge  of  ignorant  men,  who  not 
knowing  what  to  say,  and  yet  presuming  to  say  something,  do  often 
fall  upon  such  expressions". 

Digby,  like  Galileo  and  Hobbes,  wished  to  explain  all  phenomena 
by  reference  to  two  "virtues"  only,  those  of  rarity  and  density, 
"working  by  means  oflocall  Motion".  Chapters  twenty-three,  twenty- 
four,  and  twenty-five  contain  his  opinions  and  experiments  in  embryo- 
logy. He  begins  by  opening  the  question  of  epigenesis  or  preforma- 
tion, practically  for  the  first  time  since  Albert  the  Great.  "Our  main 
question  shall  be",  he  says,  "whether  they  be  framed  entirely  at 
once,  or  successively,  one  part  after  another?  And  if  this  latter  way, 
which  part  first?"  He  declares  for  epigenesis,  but  after  a  manner 
of  his  own,  refuting  "the  opinion  of  those  who  hold  that  everything 
containeth  formally  all  things".  "Why  should  not  the  parts  be  made 
in  generation",  he  asks,  "of  a  matter  like  to  that  which  maketh  them 
in  nutrition?  If  they  be  augmented  by  one  kind  of  juyce  that  after 
severall  changes  turneth  at  the  length  into  flesh  and  bone;  and  into 
every  sort  of  mixed  body  or  similar  part  whereof  the  sensitive  creature 
is  compounded,  and  that  joyneth  itself  to  what  it  findeth  there  already 
made,  why  should  not  the  same  juyce  with  the  same  progresse  of 
heat  and  moisture,  and  other  due  temperaments,  be  converted  at 
the  first  into  flesh  and  bone  though  none  be  formerly  there  to  joyn 


it  self  unto?"  He  gives  a  clearly  deterministic  account  of  develop- 
ment. "Take  a  bean,  or  any  other  seed  and  put  it  in  the  earth,  and 
let  water  fall  upon  it;  can  it  then  choose  but  that  the  bean  must  swell? 
The  bean  swelling,  can  it  choose  but  break  the  skin?  The  skin 
broken,  can  it  choose  (by  reason  of  the  heat  that  is  in  it)  but  push 
out  more  matter,  and  do  that  action  which  we  may  call  germinating? 
Can  these  germs  choose  but  pierce  the  earth  in  small  strings,  as  they 
are  able  to  make  their  way? .  .  .  Thus  by  drawing  the  thrid  carefully 
along  through  your  fingers,  and  staying  at  every  knot  to  examine 
how  it  is  tyed ;  you  see  that  this  difficult  progresse  of  the  generation 
of  living  creatures  is  obvious  enough  to  be  comprehended  and  the 
steps  of  it  set  down;  if  one  would  but  take  the  paines  and  afford 
the  time  that  is  necessary  to  note  diligently  all  the  circumstances  in 
every  change  of  it. . . .  Now  if  all  this  orderly  succession  of  mutations 
be  necessarily  made  in  a  bean,  by  force  of  sundry  circumstances  and 
externall  accidents ;  why  may  it  not  be  conceived  that  the  like  is  also 
done  in  sensible  creatures,  but  in  a  more  perfect  manner,  they  being 
perfecter  substances?  Surely  the  progresse  we  have  set  down  is  much 
more  reasonable  than  to  conceive  that  in  the  seed  of  the  male  there 
is  already  in  act,  the  substance  of  flesh,  bone,  sinews,  and  veins,  and 
the  rest  of  those  severall  similar  parts  which  are  found  in  the  body 
of  an  animall,  and  that  they  are  but  extended  to  their  due  magnitude 
by  the  humidity  drawn  from  the  mother,  without  receiving  any 
substantiall  mutation  from  what  they  were  originally  in  the  seed. 
Let  us  then  confidently  conclude,  that  all  generation  is  made  of  a 
fitting,  but  remote,  homogeneall  compounded  substance  upon  which 
outward  Agents,  working  in  the  due  course  of  Nature,  do  change  it 
into  another  substance,  quite  different  from  the  first,  and  do  make  it 
lesse  homogeneall  than  the  first  was.  And  other  circumstances  and 
agents  do  change  this  second  into  a  third,  that  third,  into  a  fourth; 
and  so  onwards,  by  successive  mutations  that  still  make  every  new 
thing  become  lesse  homogeneall  than  the  former  was,  according  to 
the  nature  of  heat,  mingling  more  and  more  different  bodies  together, 
untill  that  substance  bee  produced  which  we  consider  the  period  of 
all  these  mutations."  This  passage  is  indeed  admirable,  and  well 
expresses  the  most  modern  conception  of  embryonic  development, 
that  of  the  ovum  as  a  physico-chemical  system,  containing  within 
itself  only  to  a  slight  and  varying  degree  any  localisation  answering 
to  the  localisation  of  the  adult,  and  ready  to  change  itself,  once  the 


132  EMBRYOLOGY   IN  THE  SEVENTEENTH       [pt.  ii 

appropriate  stimulus  has  been  received,  into  the  completed  embryo 
by  the  actions  and  reactions  of  its  own  constituents  on  the  one  hand 
and  the  influence  of  the  fitting  factors  of  the  environment  upon  the 
other.  Digby  has  not  received  his  due  in  the  past;  he  stands  to 
embryology  as  an  exact  science,  much  in  the  same  relationship  as 
Bacon  to  science  as  a  whole. 

"Generation  is  not  made",  he  says,  "by  aggregation  of  like  parts 
to  presupposed  like  ones;  nor  by  a  specificall  worker  within;  but  by 
the  compounding  of  a  seminary  matter  with  the  juice  which  accrueth 
to  it  from  without  and  with  the  steams  of  circumstant  bodies,  which 
by  an  ordinary  course  of  nature  are  regularly  imbibed  in  it  by  degrees 
and  which  at  every  degree  doe  change  it  into  a  different  thing ..."  (see 
p.  317).  "Therefore  to  satisfie  ourselves  herein,  it  were  well  we  made 
our  remarks  on  some  creatures  that  might  be  continually  in  our  power 
to  observe  in  them  the  course  of  nature  every  day  and  hour.  Sir  lohn 
Heydon,  the  Lieutenant  of  his  Majesties  Ordnance  (that  generous 
and  knowing  Gentleman,  and  consummate  Souldier  both  in  theory 
and  practice)  was  the  first  that  instructed  me  how  to  do  this,  by 
means  of  a  furnace  so  made  as  to  imitate  the  warmth  of  a  sitting  hen. 
In  which  you  may  lay  severall  eggs  to  hatch,  and  by  breaking  them 
at  severall  ages  you  may  distinctly  observe  every  hourly  mutation 
in  them  if  you  please."  Sir  Kenelm  then  goes  on  to  describe  the 
events  that  take  place  in  the  incubating  egg,  which  he  does  very 
accurately,  though  briefly.  In  vivipara,  he  says,  the  like  experiments 
have  been  made,  and  the  like  conclusions  come  to  by  "that  learned 
and  exact  searcher  into  nature.  Doctor  Harvey" — these  he  must 
have  learnt  of  by  word  of  mouth,  for  Harvey's  book  had  not  at  that 
time  been  published.  As  regards  heredity,  he  adopts  a  pure  theory 
of  pangenesis,  and  has  more  to  say  about  it  than  any  other  writer 
of  his  time.  He  is  sure  that  the  heart  is  first  formed  both  in  ovipara 
and  vivipara,  "whose  motion  and  manner  of  working  evidently  ap- 
pears in  the  twinckling  of  the  first  red  spot  (which  is  the  first  change) 
in  the  egge". 

Sir  Kenelm  Digby  not  only  anticipated  the  outlook  of  the  physico- 
chemical  embryologist,  but  he  also  foreshadowed  with  considerable 
accuracy  Wilhelm  Roux's  definition  of  interim  embryological  laws. 
"Out  of  our  short  survey",  he  says,  "of  which  (anserable  to  our  weak 
talents,  and  slender  experience)  I  perswade  myselfe  it  appeareth 
evidently  enough  that  to  effect  this  worke  of  generation  there  needeth 


not  to  be  supposed  a  forming  virtue  or  Vis  Formatrix  of  an  unknown 
power  and  operation,  as  those  that  consider  things  suddenly  and  in 
grosse  do  use  to  put.  Yet  in  discourse,  for  conveniency  and  shortnesse 
of  expression  we  shall  not  quite  banish  that  terme  from  all  commerce 
with  us;  so  that  what  we  mean  by  it  be  rightly  understood,  which  is 
the  complex  assemblement,  or  chain  of  all  the  causes,  that  concur 
to  produce  this  effect,  as  they  are  set  on  foot  to  this  end  by  the  great 
Architect  and  Moderatour  of  them,  God  Almighty,  whose  instrument 
Nature  is :  that  is,  the  same  thing,  or  rather  the  same  things  so  ordered 
as  we  have  declared,  but  expressed  and  comprized  under  another 
name."  Thus  Sir  Kenelm  admits  that  it  is  allowable  to  speak  of  the 
"complex  assemblement"  of  causes,  as  if  it  were  one  formative  virtue, 
and  this  corresponds  to  Roux's  "secondary  components"  or  interim 
embryological  laws.  But  that  the  portmanteau  generalisations  can 
be  resolved  into  ultimate  physico-chemical  processes,  Digby  both 
believes  and  spends  two  entire  chapters  in  trying  to  show.  Digby 
has  been  one  of  the  two  seventeenth-century  Englishmen  most  under- 
estimated in  the  history  of  biology,  but  his  place  is  in  reality  a  very 
high  one.  How  far  he  was  in  advance  of  his  time  may  be  gauged 
from  the  work  of  his  contemporary  Sperlingen,  whose  book  of  1641 
was  thoroughly  scholastic  and  retrograde. 

His  Treatise  on  Bodies  evoked  several  answers.  Undoubtedly  the 
most  interesting  from  the  progressive  side  was  that  of  Nathaniel 
Highmore,  who  will  always  be  well  remembered  in  embryological 
history.  Highmore's  The  History  of  Generation  came  out  in  1651,  so 
that  Harvey  must  have  known  of  it,  and  it  is  one  of  the  puzzles  of 
this  period  why  Harvey  did  not  make  any  mention  of  it  in  his  work, 
especially  as  J.  D.  Horst  in  a  letter  to  Harvey  refers  to  Highmore  as  his 
pupil.  Harvey  replying  in  1655  said  he  had  not  seen  Highmore  for 
seven  years.  Highmore's  title-page  expressly  states  that  his  book  is 
an  answer  to  the  opinions  of  Sir  Kenelm  Digby.  But  before  dis- 
cussing in  what  the  answer  consisted,  we  may  look  at  the  plate  which 
is  bound  in  immediately  after  the  dedication  (to  Robert  Boyle). 
It  is  interesting  in  that  it  shows  again  the  idea  initiated  by  Leonardo, 
namely,  that  all  growing  things,  plants  as  well  as  animals,  have  an 
umbilical  cord,  and  in  that  the  drawings  of  the  chick  embryos  and 
eggs  are  more  quaint  than  accurate  (Plate  VI). 

Highmore  first  describes  the  Aristotelian  doctrine  of  form  and 
matter,  and  then  censures  both  it  and  the  extensions  of  it  with  their 

134  EMBRYOLOGY   IN  THE   SEVENTEENTH       [pt.  ii 

"qualities",  etc.,  much  as  Digby  himself  had  done.  "Some  of  our 
later  philosophers  have  showed  us  that  those  forms  w'^*^  they  thought 
and  taught  to  bee  but  potentially  in  the  matter,  are  there  actually 
subsisting  though  till  they  have  acquired  fitting  organs,  they  manifest 
not  themselves.  And  that  the  effects  which  were  done  before  their 
manifestation  (as  the  forming  and  fashioning  of  the  parts  wherein 
they  are  to  operate)  can  rise  from  nothing  else  than  from  the  Soul 
itselfe.  This  likewise  I  shall  leave  to  the  Readers  enquiry,  and  shall 
follow  that  other  way  of  introducing  Forms,  and  Generation  of 
creatures  (as  well  animals  as  vegetables)  which  gives  Fortune  and 
Chance  the  preheminency  in  that  work."  He  then  describes  Sir 
Kenelm's  opinions,  quoting  from  him  in  detail,  and  dissents  from 
them  mainly  on  the  ground  that  they  do  not  sufficiently  account 
for  embryogeny,  as  it  were,  from  a  technical  point  of  view.  That  they 
subvert  the  "antique  principals  of  philosophy"  does  not  worry 
Highmore,  but  in  his  view  their  detailed  mechanisms  do  not  explain 
the  facts,  a  much  more  serious  drawback.  Highmore  is  himself  by 
way  of  being  an  Atomist,  and  it  is  because  embryology  was  first 
treated  by  him  from  an  atomistic  standpoint  that  he  derives  his 
importance.  "The  blood,  that  all  parts  may  be  irrigated  with  its 
benigne  moisture,  is  forc'd  by  several  channels  to  run  through  every 
region  and  part  of  the  body;  by  which  meanes  every  part  out  of 
that  stream  selects  those  atomes  which  they  finde  to  be  cognate  to 
themselves.  Amongst  which  the  Testicles  abstract  some  spiritual 
atomes  belonging  to  every  part,  which  had  they  not  here  been 
anticipated,  should  have  been  attracted  to  those  parts,  to  which 
properly  they  did  belong  for  nourishment. . .  .  These  particles  passing 
through  the  body  of  the  Testicles,  and  being  in  this  Athanor  cohobated 
and  reposited  into  a  tenacious  matter,  at  last  passe  through  infinite 
Meanders  through  certain  vessels,  in  which  it  undergoes  another 
digestion  and  pelicanizing."  Highmore  objects,  therefore,  more  to 
Digby 's  theory  of  pangenesis  than  to  his  description  of  embryogenesis. 
He  goes  on  to  give  a  long  description  of  the  development  of  the  chick 
in  the  egg,  mentioning  in  passing  that  the  albumen  corresponds  to 
the  semen  and  the  blood  of  vivipara  and  the  yolk  to  their  milk. 
"Fabritius,  who  hath  taken  a  great  deal  of  pains  in  dissections.  .  . 
supposes  the  chick  to  be  formed  from  the  chalazae,  that  part  which 
by  our  Women  is  called  the  treddle.  But  this  likewise  is  false,  for 
then  every  egge  should  produce  2  chickens,  there  being  one  treddle 


l^:    j: 


9  pp  ^^^E 


■^        ^ 


0y:      6^^- 

0a:   ^f 

Tat-.  1^ 

(P^:     6. 




at  each  end  of  the  egg,  which  serve  for  no  other  end  than  for  Hga- 
ments  to  contain  the  yolk  in  an  equilibrium,  that  it  might  not  by 
every  moving  of  the  egg  be  shakt,  broke,  and  confused  with  the  white." 
Highmore  was  the  first  to  draw  attention  to  the  increase  of  brittleness 
which  takes  place  in  the  egg-shell  during  incubation,  and  he  holds 
still  to  the  Epicurean  view  that  the  female  produces  a  kind  of  seed, 
though  he  thinks  that  the  chick  embryo  is  nourished  in  the  early 
stages  by  the  amniotic  liquid. 

Perhaps  the  most  interesting  reply  to  Digby  from  the  traditional 
angle  was  that  of  Alexander  Ross.  In  his  Philosophicall  Touchstone  he 
upheld  the  Galenic  view  that  the  liver  must  be  first  formed  in  genera- 
tion, for  the  nourishment  is  in  the  blood  and  the  blood  requires  a  liver 
to  make  it :  ergo,  the  liver  must  be  the  earliest  organ.  Such  arguments 
could  dispense  with  observations.  Ross  also  mentions  Digby's  sug- 
gestion that  the  "formative  virtue"  was  only  a  bundle  of  natural 
causes,  but  he  claims  that  the  notion  was  an  old  one  in  school- 
philosophy,  being  included  in  the  phrase  causa  causae^  causa 

3-3.    Thomas  Browne  and  the  Beginnings  of  Chemical  Em- 

There  are  references  to  embryology  in  Sir  Thomas  Browne's 
Pseudodoxia  Epidemica,  or  Inquiries  into  very  many  vulgar  Tenents  and 
commonly  received  Truths,  which  was  published  at  this  time.  The 
twenty-eighth  chapter  of  the  third  book  contains  a  number  of 
difficult  problems  in  the  embryology  of  the  period,  in  most  cases 
stated  without  any  solution.  "That  a  chicken  is  formed  out  of  the 
yolk  of  the  Egg  was  the  opinion  of  some  Ancient  Philosophers. 
Whether  it  be  not  the  nutrient  of  the  Pullet  may  also  be  considered ; 
since  umbilical  vessels  are  carried  into  it,  since  much  of  the  yolk 
remaineth  after  the  chicken  is  formed,  since  in  a  chicken  newly 
hatched,  the  stomack  is  tincted  yellow  and  the  belly  full  of  yelk 
which  is  drawn  at  the  navel  or  vessels  towards  the  vent,  as  may  be 
discerned  in  chickens  a  day  or  two  before  exclusion.  Whether  the 
chicken  be  made  out  of  the  white,  or  that  be  not  also  its  aliment, 
is  likewise  very  questionable,  since  an  umbilical  vessel  is  derived  unto 
it,  since  after  the  formation  and  perfect  shape  of  the  chicken,  much 
of  the  white  remaineth.  Whether  it  be  not  made  out  of  the  grando, 
gallature,  germ,  or  tred  of  the  egg,  as  Aquapendente  informeth  us, 

136  EMBRYOLOGY   IN  THE   SEVENTEENTH       [pt.  11 

seemed  to  many  of  doubt;  for  at  the  blunter  end  it  is  not  discovered 
after  the  chicken  is  formed,  by  this  also  the  white  and  the  yelk  are 
continued  whereby  it  may  conveniently  receive  its  nutriment  from 
them  both.. .  .But  these  at  last  and  how  in  the  Cicatricula  or  little 
pale  circle  formation  first  beginneth,  how  the  Grando  or  tredle,  are 
but  the  poles  and  establishing  particles  of  the  tender  membrans 
firmly  conserving  the  floating  parts  in  their  proper  places,  with  many 
observables,  that  ocular  Philosopher  and  singular  discloser  of  truth, 
Dr  Harvey  hath  discovered,  in  that  excellent  discourse  of  generation, 
so  strongly  erected  upon  the  two  great  pillars  of  truth,  Experience, 
and  Reason. 

"That  the  sex  is  discernable  from  the  figure  of  eggs,  or  that  cocks 
or  hens  proceed  from  long  or  round  ones,  experiment  will  easily 
frustrate..  .  .Why  the  hen  hatcheth  not  the  egg  in  her  belly?  Why 
the  egg  is  thinner  at  one  extream?  Why  there  is  some  cavity  or 
emptiness  at  the  blunter  end?  Why  we  open  them  at  that  part? 
Why  the  greater  end  is  first  excluded  [cf  p.  233]?  Why  some  eggs 
are  all  red,  as  the  Kestrils,  some  only  red  at  one  end,  as  those  of 
kites  and  buzzards?  Why  some  eggs  are  not  oval  but  round,  as 
those  of  fishes  ?  etc.  are  problems  whose  decisions  would  too  much 
enlarge  this  discourse."  And  elsewhere,  "That  (saith  Aristotle)  which 
is  not  watery  and  improlifical  will  not  conglaciate;  which  perhaps 
must  not  be  taken  strictly,  but  in  the  germ  and  spirited  particles; 
for  Eggs,  I  observe,  will  freeze,  in  the  albuginous  part  thereof". 
Again,  "They  who  hold  that  the  egg  was  before  the  bird,  prevent 
this  doubt  in  many  other  animals,  which  also  extendeth  unto  them; 
for  birds  are  nourished  by  umbilical  vessels  and  the  navel  is  manifest 
sometimes  a  day  or  two  after  exclusion..  .  .The  same  is  made  out 
in  the  eggs  of  snakes,  and  is  not  improbable  in  the  generation  of 
Porwiggles  or  Tadpoles,  and  may  also  be  true  in  some  vermiparous 
exclusions,  although  (as  we  have  observed  in  the  daily  progress  of 
some)  the  whole  Magot  is  little  enough  to  make  a  fly  without  any 
part  remaining. .  .  .  The  vitreous  or  glassie  flegm  of  white  of  egg  will 
thus  extinguish  a  coal." 

These  citations  show  Sir  Thomas  to  have  been  more  than  simply 
the  supreme  artist  in  English  prose  which  is  his  common  title  to 
remembrance.  In  picking  his  way  carefully  among  the  doubtful 
points  and  difficult  problems  which  previous  embryologists  had  pro- 
pounded but  not  answered,  he  usually  managed  to  give  the  right 


answer  to  each.  But  in  addition  to  this,  he  was  also  an  experimentahst, 
he  had  made  both  anatomical  and  physical  experiments  on  eggs, 
and  he  was  prepared  to  put  any  disputed  point  to  the  test  of  "ocular 
aspection",  if  this  could  be  done.  His  experimental  contributions 
to  embryology  come  out  more  clearly  in  his  Commonplace  Books  which 
were  published  by  Wilkin  in  1836. 

"Runnet  beat  up  with  the  whites  of  eggs  seems  to  perform  nothing, 
nor  will  it  well  incorporate,  without  so  much  heat  as  will  harden 
the  tgg. .  .  .  Eggs  seem  to  contain  within  themselves  their  own 
coagulum,  evidenced  upon  incubation,  which  makes  incrassation  of 
parts  before  very  fluid..  .  .Rotten  eggs  will  not  be  made  hard  by 
incubation  or  decoction,  as  being  destitute  of  that  spirit  or  having 
the  same  vitiated. .  .  .  They  will  be  made  hard  in  oil  but  not  so  easily 
in  vinegar  which  by  the  attenuating  quality  keeps  them  longer  from 
concoction,  for  infused  in  vinegar  they  lose  the  shell  and  grow  big 
and  much  heavier  then  before. ...  In  the  ovary  or  second  cell  of  the 
matrix  the  white  comes  upon  the  yolk,  and  in  the  later  and  lower 
part,  the  shell  is  made  or  manifested.  Try  if  the  same  parts  will  give 
any  coagulation  unto  milk.  Whether  will  the  ovary  best?... The 
whites  of  eggs  drenched  in  saltpeter  will  shoot  forth  a  long  and  hairy 
saltpeter  and  the  egg  become  of  a  hard  substance.  Even  in  the  whole 
egg  there  seems  a  great  nitrosity,  for  it  is  very  cold  and  especially 
that  which  is  without  a  shell  (as  some  are  laid  by  fat  hens)  or  such 
as  are  found  in  the  egg  poke  or  lowest  part  of  the  matrix,  if  an  hen 
be  killed  a  day  or  two  before  she  layeth. .  .  .  Difference  between  the 
sperm  of  frogs  and  eggs,  spawn  though  long  boiled,  would  not  grow 
thick  and  coagulate.  In  the  eggs  of  skates  or  thornbacks  the  yolk 
coagulates  upon  long  docoction,  not  the  greatest  part  of  the  white. .  .  . 
In  spawn  of  frogs  the  little  black  specks  will  concrete  though  not  the 
other. ...  In  eggs  we  observe  the  white  will  totally  freeze,  the  yolk,  with 
the  same  degree  of  cold  will  grow  thick  and  clammy  like  the  gum  of 
trees,  but  the  sperm  or  tread  hold  its  former  body,  the  white  growing 
stiff  that  is  nearest  to  it." 

The  only  conclusion  that  can  be  drawn  from  these  remarkable 
observations  is  that  it  was  in  the  "  laboratory "  in  Sir  Thomas'  house 
at  Norwich  that  the  first  experiments  in  chemical  embryology  were 
undertaken.  His  significance  in  this  connection  has  so  far  been  quite 
overlooked,  and  it  is  time  to  recognise  that  his  originality  and  genius 
in  this  field  shows  itself  to  be  hardly  less  remarkable  than  in  so  many 

138  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  11 

others.  To  have  occupied  himself  with  the  chemical  properties  of 
those  substances  which  afford  the  raw  material  of  development  was 
a  great  step  for  those  times,  but  it  was  not  until  some  twenty-five 
years  later  that  Walter  Needham  carried  this  new  interest  into  the 
mammalian  domain,  and  made  chemical  experiments  there. 

3-4.    William  Harvey 

The  Latin  edition  of  William  Harvey's  book  on  the  generation  of 
animals  appeared  in  1651,  and  the  English  in  1653.  The  frontispiece 
of  the  former  which  is  reproduced  as  the  frontispiece  of  this  book  is 
a  very  noteworthy  picture,  and  derives  a  special  interest  from  the 
fact  that  on  the  egg  which  Zeus  holds  in  his  hands  is  written,  "^x 
ovo  omnia'\ — a  conception  which  Harvey  is  continually  expounding 
(see  especially  the  chapter,  "That  an  egg  is  the  common  Original 
of  all  animals"),  but  which  he  never  puts  into  epigrammatic  form 
in  his  text,  so  that  the  saying,  omne  vivum  ex  ovo,  often  attributed 
to  him,  is  only  obliquely  his. 

The  De  Generatione  Animalium  was  written  at  different  times  during 
his  life,  and  not  collected  together  for  publication  until  George  Ent, 
of  the  College  of  Physicians,  persuaded  Harvey  to  give  it  forth  about 
1650.  As  early  as  1625  Harvey  was  studying  the  phenomena  of 
embryology,  as  is  shown  among  other  evidences  by  a  passage  in  his 
book  where  he  says,  "Our  late  Sovereign  King  Charles,  so  soon  as 
he  was  become  a  man,  was  wont  for  Recreation  and  Health  sake, 
to  hunt  almost  every  week,  especially  the  Buck  and  Doe,  no  Prince 
in  Europe  having  greater  store,  whether  wandring  at  liberty  in  the 
Woods  and  Forrests  or  inclosed  and  kept  up  in  Parkes  and  Chaces. 
In  the  three  summer  moneths  the  Buck  and  the  Stagge  being  then 
fat  and  in  season  were  his  game,  and  the  Doe  and  Hind  in  the 
Autumme  and  Winter  so  long  as  the  three  seasonable  moneths  con- 
tinued. Hereupon  I  had  a  daily  opportunity  of  dissecting  them  and 
of  making  inspection  and  observation  of  all  their  parts,  which  liberty 
I  chiefly  made  use  of  in  order  to  the  genital  parts".  Nor  was  Harvey 
less  diligent  in  examining  the  generation  of  ovipara.  John  Aubrey, 
in  his  Brief  Lives,  says,  "  I  first  sawe  Doctor  Harvey  at  Oxford  in  1642 
after  Edgehill  fight,  but  I  was  then  too  young  to  be  acquainted  with 
so  great  a  Doctor.  I  remember  that  he  came  often  to  Trin.  Coll. 
to  one  George  Bathurst,  B.D.  who  kept  a  hen  in  his  chamber  to 


hatch  egges,  which  they  did  dayly  open  to  discerne  the  progress 
and  way  of  generation".  Aubrey  mentions  a  conversation  he  had  with 
a  sow-gelder,  a  countryman  of  Httle  learning,  but  much  practical 
experience  and  wisdom,  who  told  him  that  he  had  met  Dr  Harvey, 
who  had  conversed  with  him  for  two  or  three  hours,  and  "if  he  had 
been",  the  man  remarked,  "as  stiff  as  some  of  our  starched  and 
formall  doctors,  he  had  known  no  more  than  they".  Harvey  seems 
also  to  have  learnt  all  he  could  from  the  keepers  of  King  Charles' 
forests,  as  several  passages  in  his  book  show.  Nor  was  the  King's  own 
interest  lacking.  "I  saw  long  since  a  foetus",  he  says,  "the  magnitude 
of  a  peasecod  cut  out  of  the  uterus  of  a  doe,  which  was  complete 
in  all  its  members  &  I  showed  this  pretty  spectacle  to  our  late  King 
and  Queen.  It  did  swim,  trim  and  perfect,  in  such  a  kinde  of  white, 
most  transparent  and  crystalline  moysture  (as  if  it  had  been  treasured 
up  in  some  most  clear  glassie  receptacle)  about  the  bignesse  of  a 
pigeon's  Ggge,  and  was  invested  with  its  proper  coat."  And,  again — 
"My  Royal  Master,  whose  Physitian  I  was,  was  himself  much 
delighted  in  this  kinde  of  curiosity,  being  many  times  pleased  to  be 
an  eye-witness,  and  to  assert  my  new  inventions". 

Harvey's  book  is  composed  of  seventy-two  exercitations,  which 
may  be  divided  up  for  convenience  into  five  divisions.  In  Nos.  i 
to  10  he  speaks  of  the  anatomy  and  physiology  of  the  genital  organs 
of  the  fowl,  and  the  manner  of  production  of  eggs.  Nos.  11  to  13 
and  also  Nos.  23  and  36  deal  with  the  hen's  egg  in  detail,  describing 
its  parts  and  their  uses,  while  in  Nos.  14  to  23  the  process  of  the 
"generation  of  the  foetus  out  of  the  hen  egge''  is  described.  The 
greater  part  of  the  book,  comprising  Nos.  25  to  62,  as  well  as  Nos.  71 
and  72,  is  theoretical,  and  treats  of  the  embryological  theories  held 
by  Aristotle  on  the  one  hand,  and  the  physicians,  following  Galen, 
on  the  other,  instead  of  which  it  propounds  new  views  upon  the 
subject.  Finally,  Nos.  63  to  70,  as  well  as  the  two  appendices^  or 
"particular  discourses",  are  concerned  with  embryogenesis  in  vivi- 
parous animals,  especially  in  hinds  and  does. 

It  will  be  best  to  refer  to  certain  details  and  main  points  of  interest 
in  Harvey's  discussions,  before  trying  to  assess  his  principal  contribu- 
tions to  the  science  as  a  whole.  Harvey  is  the  first,  since  Aristotle, 
to  refer  to  the  "white  yolk"  of  birds.  "For  between  the  yolk",  he 
says,  "which  is  yet  in  the  cluster  and  that  which  is  in  the  midst  of 
the  eg  when  it  is  perfected  this  is  the  difference  in  chief,  that  though 

140  EMBRYOLOGY   IN  THE   SEVENTEENTH       [pt.  ii 

the  former  be  yellowish  in  colour  and  in  appearance,  yet  its  con- 
sistence representeth  rather  the  white,  and  being  sodden,  thickeneth 
like  it,  growing  compact  and  viscous  and  may  be  cut  into  slices.  But 
the  yolk  of  a  perfect  eggc  being  boiled  groweth  friable  and  of  a  more 
earthy  consistence,  not  thick  and  glutinous  like  the  white."  All  of 
Harvey's  observations  on  the  formation  of  the  egg  in  the  oviduct 
contained  in  this  chapter  are  interesting,  and  may  with  advantage 
be  compared  with  the  studies  of  Riddle  upon  the  same  subject,  where 
the  chemical  explanation  will  be  found  for  many  of  Harvey's  simple 
observations.  Harvey's  controversy  with  Fabricius  on  the  question 
of  whether  the  egg  is  produced  with  a  hard  shell  or  only  acquires 
its  external  hardness  upon  standing  in  the  air,  which  follows  im- 
mediately on  the  above  citation,  is  interesting.  "Fabricius  seemeth 
to  me  to  be  in  errour,  for  though  I  was  never  so  good  at  slight  of 
hand  to  surprise  an  egge  in  the  very  laying,  and  so  make  discovery 
whether  it  was  soft  or  hard,  yet  this  I  confidently  pronounce  that  the 
shell  is  compounded  within  the  womb  of  a  substance  there  at  hand 
for  the  purpose,  and  that  it  is  framed  in  the  same  manner  as  the 
other  parts  of  the  egg  are  by  the  plastick  faculty,  and  the  rather, 
because  I  have  seen  an  exceeding  small  egge  which  had  a  shell  of 
its  own  and  yet  was  contained  within  another  egge,  greater  and 
fairer  than  it,  which  egge  had  a  shell  too." 

Harvey  was  the  first  to  note  that  the  white  of  the  hen's  egg  is 
heterogeneous,  in  the  sense  that  part  of  it  is  much  more  liquid  than 
the  rest,  and  that  the  more  viscous  part  seems  to  be  contained  in  an 
exceedingly  fine  membrane,  so  that  if  it  is  sliced  across  with  a  knife, 
its  contents  will  flow  out.  He  also  set  right  the  errors  of  Fabricius, 
Parisanus  and  others,  by  showing  that  the  chalazae  were  neither  the 
seed  of  the  cock  nor  the  material  out  of  which  the  embryo  was  formed, 
and,  most  important  of  all,  by  demonstrating  that  the  cicatricula 
was  the  point  of  origin  of  the  embryo.  He  denied,  as  against  popular 
belief,  that  the  hen  contributed  anything  to  the  developing  egg  but 
heat,  "For  certain  it  is  that  the  chicken  is  constituted  by  an  internal 
principle  in  the  egge,  and  that  there  is  no  accession  to  a  complete 
and  perfect  egge  by  the  Hennes  incubation,  but  bare  cherishing  and 
protection;  no  more  than  the  Hen  contributeth  to  the  chickens 
which  are  now  hatched,  which  is  only  a  friendly  heat,  and  care,  by 
which  she  defendeth  them  from  the  cold,  and  forreign  injuries  and 
helpeth  them  to  their  meat".  Whether  future  work  will  still  affirm 


that  nothing  is  given  to  the  egg  by  the  hen  except  heat  is  beginning 
now  to  be  in  doubt,  if  the  results  of  Chattock  are  correct. 

In  the  description  of  the  development  of  the  embryo  in  the  hen's 
egg,  which  remains  to  this  day  one  of  the  most  accurate,  Harvey 
says  with  regard  to  the  spot  on  the  yolk,  which  had,  of  course,  been 
seen  and  mentioned  by  many  previous  observers,  "And  yet  I  con- 
ceive that  no  man  hitherto  hath  acknowledged  that  this  Cicatricula 
was  to  be  found  in  every  egge  nor  that  it  was  the  first  Principle  of 
the  Egge".  His  description  of  the  beginning  of  the  heart,  that 
"capering  bloody  point"  or  "punctum  saliens'\  is  too  famous  to 
need  more  than  a  reference.  He  thought  that  the  amniotic  liquid 
was  of  "mighty  use",  "For  while  the  embryos  swim  there,  they  are 
guarded  and  skreened  from  all  concussion,  contusion,  and  other  out- 
ward injuries,  and  are  also  nourished  by  it". 

Thus  he  made  no  advance  on  the  opinion  which  had  for  long  been 
held,  namely,  that  the  amniotic  liquid  or  colliquamentum  served 
for  sustenance.  "I  believe",  he  says,  "that  this  colliquamentum  or 
water  wherein  the  foetus  swims  doth  serve  for  his  sustenance  and 
that  the  thinner  and  purer  part  of  it,  being  imbibed  by  the  umbilicall 
vessels,  does  constitute  and  supply  the  primo-genital  parts,  and  the 
rest,  like  Milk,  being  by  suction  conveyed  into  the  stomack  and  there 
concocted  or  chylified,  and  afterwards  attracted  by  the  orifices  of 
the  Meseraick  Veins  doth  nourish  and  enlarge  the  tender  embryo." 
His  arguments  for  this  are,  ( i )  that  swallowing  movements  take  place, 
and  (2)  that  the  gut  of  the  chicken  is  "stuft"  with  excrement  which 
could  hardly  arise  from  any  other  source.  He  was  thus  led  to  divide 
the  amniotic  liquid  into  two  quite  imaginary  constituents,  a  purer 
and  "sincerer"  part,  which  could  be  absorbed  straight  into  the  blood 
without  chylification,  and  a  creamless  milky  part  which  could  not 
be  treated  so  simply. 

"About  the  fourth  day",  says  Harvey,  "the  egg  beginneth  to  step 
from  the  life  of  a  plant  to  that  of  an  animall."  "From  that  to  the 
tenth  it  enjoys  a  sensitive  and  moving  soul  as  Animals  do,  and  after 
that,  it  is  compleated  by  degrees  and  being  adorned  with  Plumes, 
Bill,  Clawes  and  other  furniture,  it  hastens  to  get  out."  These  and 
other  passages  which  deal  with  the  forerunner  of  the  theory  of  re- 
capitulation are  interesting,  but  we  have  already  met  essentially  the 
same  idea  in  Aristotle.  Harvey  contributed  nothing  new  to  it.  The 
first  point  on  which  he  went  definitely  wrong  was  the  statement  that 

142  EMBRYOLOGY   IN   THE   SEVENTEENTH        [pt.  ii 

he  made  that  the  heart  does  not  pulsate  before  the  appearance  of 
the  blood.  No  doubt  his  lack  of  microscopical  facilities  or  of  the 
desire  to  use  them  affords  the  reason  for  this  error,  but  it  was  a  very 
unfortunate  one,  for  it  was  to  a  large  extent  upon  it  that  he  formulated 
his  doctrine  "the  life  is  in  the  blood".  For  example,  he  says,  "I  am 
fully  satisfied  that  the  Blood  hath  a  being  before  any  other  part  of  the 
body  besides,  and  is  the  elder  brother  to  all  other  parts  of  the  foetus ". 

The  yolk,  Harvey  thought,  supplied  the  place  of  milk,  "and  is 
that  which  is  last  consumed,  for  the  remainder  of  it  (after  the  chicken 
is  hatched  and  walks  abroad  with  the  Henne)  is  yet  contained  in  its 
belly".  He  thus  ranged  himself  with  Alcmaeon  and  Abderhalden. 
All  his  remarks  about  the  relationships  of  yolk  and  white  in  nutrition 
are  worth  consideration;  in  noting,  for  instance,  that  the  yolk  is 
the  last  to  be  consumed,  he  comes  very  near  to  anticipating  the 
knowledge  of  the  succession  of  energy-sources  which  we  now  possess 
(see  Section  T"]).  "In  that  Physitians  affirme,  that  the  Yolke  is  the 
hotter  part  of  the  ^gg&,  and  the  most  nourishing,  I  conceive  that  they 
understand  it,  in  relation  to  us,  as  it  is  become  our  nourishment, 
not  as  it  doth  supply  more  congruous  aliment  to  the  chicken  in  the 
tggt.  And  this  appeares  out  of  our  history  of  the  Fabrick  of  the 
chicken ;  which  doth  first  prey  upon  and  devoure  the  thinner  part  of 
the  white,  before  the  grosser;  as  it  were  a  more  proper  diet,  and  did 
more  easily  submit  to  transmutation  into  the  substance  of  the  foetus. 
And  therefore  the  yolke  seems  to  be  a  remoter  and  more  deferred 
entertainment  than  the  white;  for  all  the  white  is  quite  and  clean 
spent,  before  any  notable  invasion  is  made  upon  the  yolke."  A  com- 
parison between  these  simple  facts  and  our  knowledge  of  embryonic 
nutrition  is  most  interesting  (see  Section  6-9). 

In  connection  with  Minot's  distinction  of  the  periods  of  embryonic 
growth,  it  is  curious  that  Harvey  says,  "And  now  the  foetus  moves 
and  gently  tumbles,  and  stretcheth  out  the  neck  though  nothing  of 
a  brain  be  yet  to  be  seen,  but  merely  a  bright  water  shut  up  in  a  small 
bladder.  And  now  it  is  a  perfect  Magot,  differing  only  from  those 
kinde  of  wormes  in  this,  that  those  when  they  have  their  freedom 
crawle  up  and  down  and  search  for  their  living  abroad,  but  this 
worm  constant  to  his  station,  and  swimming  in  his  own  provision, 
draws  it  in  by  his  Umbilicall  Vessels". 

Sometimes  Harvey  confesses  himself  puzzled  by  problems  which 
could  only  be  solved  by  chemical  means,  yet  it  does  not  occur  to 


him  that  this  is  the  case.  For  instance,  he  enquires  why  heat  will 
develop  a  chick  out  of  a  good  egg  but  will  only  make  a  bad  one  worse. 
"Give  me  leave  to  add  something  here",  he  writes,  "which  I  have 
tried  often;  that  I  might  the  better  discerne  the  scituation  of  the 
foetus  and  the  liquors  at  the  seventeenth  day  to  the  very  exclusion. 
I  have  boiled  an  eggc  till  it  grew  hard,  and  then  pilling  away  the 
shell  and  freeing  the  scituation  of  the  chicken,  I  found  both  the 
remaining  parts  of  the  white,  and  the  two  parts  of  the  yolk  of  the 
same  consistence,  colour,  tast,  and  other  accidents,  as  any  other  stale 
egge,  thus  ordered,  is.  And  upon  this  Experiment,  I  did  much  ponder 
whence  it  should  come  to  passe  that  Improlifical  eggs  should,  from 
the  adventitious  heat  of  a  sitting  Henne,  putrifie  and  stink;  and  yet 
no  such  inconvenience  befall  the  Prolifical.  But  both  these  liquors 
(though  there  be  a  Chicken  in  them  too,  and  he  with  some  pollution 
and  excrement)  should  be  found  wholesome  and  incorrupt;  for  that 
if  you  eat  them  in  the  dark  after  they  are  boyled,  you  cannot  dis- 
tinguishe  them  from  egges  that  are  so  prepared,  which  have  never 
undergone  the  hen's  incubation."  Harvey  was  never  afraid  of  trying 
such  tests  on  himself;  in  another  place,  for  example,  he  says,  "Eggs 
after  2  or  3  days  incubation,  are  even  then  sweeter  relished  than  stale 
ones  are,  as  if  the  cherishing  warmth  of  the  hen  did  refresh  and 
restore  them  to  their  primitive  excellence  and  integrity".  "And  the 
yolke  (at  14  days)  was  as  sweet  and  pleasant  as  that  of  a  newlaid 
cgge,  when  it  is  in  like  manner  boyled  to  an  induration."  Another 
matter  on  which  Harvey  set  Fabricius  right  was  on  the  question 
whether  at  hatching  the  hen  helps  the  chicken  out  or  the  chicken 
comes  out  by  itself.  The  latter  was  the  belief  held  by  Harvey,  who 
said  of  Fabricius'  arguments  on  this  point  that  they  were  "pleasant 
and  elegant,  but  not  well  bottomed". 

On  the  great  question  of  preformation  v.  epigenesis,  Harvey  keenly 
argued  in  favour  of  the  latter  view.  "There  is  no  part  of  the  future 
foetus  actually  in  the  egg,  but  yet  all  the  parts  of  it  are  in  it  poten- 
tially. ...  I  have  declared  that  one  thing  is  made  out  of  another  two 
several  wayes  and  that  as  well  in  artificial  as  natural  productions, 
but  especially  in  the  generation  of  animals.  The  first  is,  when  one 
thing  is  made  out  of  another  thing  that  is  pre-existent,  and  thus  a 
Bedstead  is  made  out  of  Timber,  and  a  Statue  out  of  a  Rock,  where 
the  whole  matter  of  the  future  fabrick  was  existent  and  in  being, 
before  it  was  reduced  into  its  subsequent  shape,  or  any  tittle  of  the 

144  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

designe  begun.  But  the  other  way  is  when  the  matter  is  both  made 
and  receiveth  its  form  at  the  same  time. ...  So  Hkewise  in  the  Genera- 
tion of  Animals,  some  are  formed  and  transfigured  out  of  matter 
already  concocted  and  grown  and  all  the  parts  are  made  and  dis- 
tinguished together  per  metamorphosin,  by  a  metamorphosis,  so 
that  a  complete  animal  is  the  result  of  that  generation;  but  some 
again,  having  one  part  made  before  another,  are  afterwards  nourished, 
augmented,  and  formed  out  of  the  same  matter,  that  is,  they  have 
parts,  whereof  some  are  before,  and  some  after,  other,  and  at  the 
same  time,  are  both  formed,  and  grow. .  .  .  These  we  say  are  made 
per  epigenesin,  by  a  post-generation,  or  after-production,  that  is 
to  say,  by  degrees,  part  after  part,  and  this  is  more  properly  called 
a  Generation,  than  the  former. .  .  .  The  perfect  animals,  which  have 
blood,  are  made  by  Epigenesis,  or  superaddition  of  parts,  and  do 
grow,  and  attain  their  just  future  or  ciKfir}  after  they  are  born. . . .  An 
animal  produced  by  Epigenesis,  attracts,  prepares,  concocts,  and 
applies,  the  Matter  at  the  same  time,  and  is  at  the  same  time  formed, 
and  augmented..  .  .Wherefore  Fabricius  did  erroniously  seek  after 
the  Matter  of  the  chicken  (as  it  were  some  distinct  part  of  the  egg 
which  went  to  the  imbodying  of  the  chicken)  as  though  the  genera- 
tion of  the  chicken  were  effected  by  a  Metamorphosis,  or  trans- 
figuration of  some  collected  lump  or  mass,  and  that  all  the  parts  of 
the  body,  at  least  the  Principall  parts,  were  wrought  off  at  a  heat 
or  (as  himselfe  speaks)  did  arise  and  were  corporated  out  of  the 
same  Matter."  Nothing  could  be  more  plain  than  Harvey's  teaching 
on  epigenesis,  so  that  he  has  precedence  over  Caspar  Wolff  on  this 

On  the  relation  between  growth  and  differentiation  Harvey  has 
some  valuable  things  to  say.  The  term  "nutrition"  he  restricted  to 
that  which  replaces  existent  structures,  and  the  term  "augmenta- 
tion" or  "increment"  to  that  which  contributes  something  new.  That 
process  which  led  to  greater  diversity  of  form  and  complexity  of  shape 
he  called  "formation"  or  "framing".  "For  though  the  head  of  the 
Chicken,  and  the  rest  of  its  Trunck  or  Corporature  (being  first  of 
a  similar  constitution)  do  resemble  a  Mucus  or  soft  glewey  substance; 
out  of  which  afterwards  all  the  parts  are  framed  in  their  order;  yet 
by  the  same  Operatour  they  are  together  made  and  augmented,  and 
as  the  substance  resembling  glew  doth  grow,  so  are  the  parts  dis- 
tinguished. Namely  they  are  generated,  altered,  and  formed  at  once, 


they  are  at  once  similar  and  dissimilar,  and  from  a  small  similar  is 
a  great  organ  made."  Harvey  was  thus  very  certain  that  the  processes 
of  growth  in  size  and  differentiation  in  shape  went  on  quite  con- 
currently, though  he  had  no  inkling  of  changes  in  the  relative  rapidity 
of  each  process.  On  this  point  he  goes  further  than  Fabricius. 
Fabricius  thought  that  growth  was  a  more  or  less  mechanical  process, 
taking  its  origin  from  the  properties  of  elementary  substances,  but 
that  differentiation  was  brought  about  by  some  more  spiritual  or 
subtle  activity.  "Fabricius",  says  Harvey,  "affirmes  amisse,  that 
the  Immutative  Faculty  doth  operate  by  the  qualities  of  the  elements, 
namely.  Heat,  Gold,  Moisture,  and  Dryness  (as  being  its  instruments) 
but  the  Formative  works  without  them  and  after  a  more  divine 
manner;  as  if  (forsooth)  she  did  finish  her  task  with  Meditation, 
Choice,  and  Providence.  For  had  he  looked  deeper  into  the  thing, 
he  would  have  seen  that  the  Formative  as  well  as  the  Alterative 
Faculty  makes  use  of  Hot,  Cold,  Moist,  and  Dry,  (as  her  instruments) 
and  would  have  deprehended  as  much  divinity  and  skill  in  Nutrition 
and  Immutation  as  in  the  operations  of  the  Formative  Faculty  her 
self."  "I  say  the  Concocting  and  Immutative,  the  Nutritive  and 
Augmenting  Faculties  (which  Fabricius  would  have  to  busie  them- 
selves only  about  Hot,  Cold,  Moist,  and  Dry,  without  all  knowledge) 
do  operate  with  as  much  artifice,  and  as  much  to  a  designed  end,  as 
the  Formative  faculty,  which  he  affirms  to  possess  the  knowledge 
and  fore-sight  of  the  future  action  and  use  of  every  particular  part 
and  organ."  Thus  although  in  nearly  every  respect  Harvey  makes  an 
advance  on  Fabricius,  yet  here  he  is  retrograde,  for,  in  the  former's 
thought,  the  growth  process  at  least  had  struggled  towards  a  deter- 
ministic schema;  with  Harvey  this  movement  is  rigidly  suppressed. 
"All  things  are  full  of  deity"  {Jovis  omnia  plena),  said  he,  "so  also  in 
the  little  edifice  of  a  chicken,  and  all  its  actions  and  operations,  Digitus 
Dei,  the  Finger  of  God,  or  the  God  of  Nature,  doth  reveal  himself" 

There  can  be  no  doubt  that  Harvey's  leanings  were  vitalistic.  In 
the  following  passage,  he  argues  against  both  those  who  wished  to 
deduce  generation  from  properties  of  bodies  (like  Sir  Kenelm  Digby) 
and  the  Atomists ;  in  other  words,  against  the  outlook  of  those  types 
of  mind  which  in  later  times  were  to  build  up  biophysics  and  bio- 
chemistry. Aubrey  notes  that  Harvey  was  "disdainfull  of  the  chymists 
and  undervalued  them". 

"It  is  the  usual  error  of  philosophers  of  these  times",  says  he,  "to 

146  EMBRYOLOGY   IN  THE   SEVENTEENTH       [pt.  11 

seek  the  diversity  of  the  causes  of  parts  out  of  the  diversity  of  the 
matter  from  whence  they  should  be  framed.  So  Physicians  affirm, 
that  the  different  parts  of  the  body  are  fashioned  and  nourished  by 
the  different  materials  of  blood  or  seed ;  namely  the  softer  parts,  as 
the  flesh,  out  of  a  thinner  matter,  and  the  more  earthy  parts  as  the 
bones,  out  of  grosser  and  harder.  But  this  error  now  too  much 
received,  we  have  confuted  in  another  place.  Nor  are  they  lesse 
deceived  who  make  all  things  out  of  Atomes,  as  Democritus,  or  out 
of  the  elements,  as  Empedocles.  As  if  (forsooth)  Generation  were 
nothing  in  the  world,  but  a  meer  separation,  or  Collection,  or  Order 
of  things.  I  do  not  indeed  deny  that  to  the  Production  of  one  thing 
out  of  another,  these  forementioned  things  are  requisite,  but  Genera- 
tion her  self  is  a  thing  quite  distinct  from  them  all.  (I  finde  Aristotle 
in  this  opinion)  and  I  my  self  intend  to  clear  it  anon,  that  out  of 
the  same  White  of  the  Egge  (which  all  men  confesse  to  be  a  similar 
body,  and  without  diversity  of  parts)  all  and  every  the  parts  of  the 
chicken  whether  they  be  Bones,  Clawes,  Feathers,  Flesh,  or  what 
ever  else,  are  procreated  and  fed.  Besides,  they  that  argue  thus 
assigning  only  a  material  cause,  deducing  the  causes  of  Natural 
things  from  an  involuntary  or  casual  concurrence  of  the  Elements, 
or  from  the  several  disposition  or  contriving  of  Atomes ;  they  doe 
not  reach  that  which  is  chiefly  concerned  in  the  operations  of  nature, 
and  in  the  Generation  and  Nutrition  of  animals,  namely  the  Divine 
Agent,  and  God  of  Nature,  whose  operations  are  guided  with  the 
highest  Artifice,  Providence,  and  Wisdome,  and  doe  all  tend  to  some 
certaine  end,  and  are  all  produced,  for  some  certaine  good.  But  these 
men  derogate  from  the  Honour  of  the  Divine  Architect,  who  hath 
made  the  Shell  of  the  Egge  with  as  much  skill  for  the  egge's  defence 
as  any  other  particle,  disposing  the  whole  out  of  the  same  matter 
and  by  one  and  the  same  formative  faculty."  But  although  these  are 
Harvey's  theories,  it  is  significant  that  in  his  preface  he  says,  "Every 
inquisition  is  to  be  derived  from  its  causes,  and  chiefly  from  the 
material  and  efficient",  thus  expressly  excluding  formal  and  final 
considerations.  Certainly,  as  far  as  his  practical  work  went,  he  was 
unaffected  by  them,  and  in  the  case  of  the  egg-shell,  for  example, 
Harvey  was  not  the  man  to  say,  "it  is  present  for  the  protection  of 
the  embryo",  and  then  to  do  or  say  nothing  more.  Such  an  explana- 
tion, though  he  might  gladly  accept  it,  was  no  bar  to  further  explora- 
tion both  by  way  of  experiment  and  observation. 


Harvey  not  only  follows  Aristotle  in  his  good  discoveries  and  true 
statements  about  the  egg,  but  also,  unfortunately,  in  his  less  useful 
parts,  as,  for  example,  when  he  devotes  several  pages  to  the  dis- 
cussion of  how  far  the  egg  itself  is  alive,  and  whether  there  is  any  soul 
in  subventaneous  or  unfruitful  eggs.  He  decides  that  there  is  only 
a  vegetative  soul.  On  the  other  hand,  he  admirably  refutes  the 
opinion  of  those  physicians — who  were  not  few  in  number — who 
declared  that  the  foetal  organs  were  all  functionless  during  foetal  life. 
"But  while  they  contende",  he  says,  "that  the  mother's  Blood  is 
the  nutriment  of  the  foetus  in  the  womb,  especially  of  the  Partes 
Sanguineae,  the  bloody  parts  (as  they  call  them)  and  that  the  Foetus 
is  at  first,  as  if  it  were  a  part  of  the  mother,  sustained  by  her  blood 
and  quickened  by  her  spirits,  in  so  much  that  the  heart  beats  not 
and  the  liver  sanguifies  not,  nor  any  part  of  the  Foetus  doth  execute 
any  publick  function,  but  all  of  them  make  Holy-Day  and  lie  idle; 
in  this  Experience  itself  confutes  them.  For  the  chicken  in  the  egge 
enjoyes  his  own  Blood,  which  is  bred  of  the  liquors  contained  within 
the  egge,  and  his  Heart  hath  its  motion  from  the  very  beginning, 
and  he  borroweth  nothing,  either  blood  or  spirits,  from  the  Hen, 
towards  the  constitution  either  of  the  sanguineous  parts  or  plumes, 
as  those  that  strictly  observe  it  may  plainly  perceive."  We  have  already 
seen  how  the  Stoics  in  antiquity  believed  that  the  embryo  was  a  part 
of  the  mother  until  it  was  born ;  from  this  idea  the  transition  would 
be  easy  to  the  belief  that  all  the  organs  in  the  embryo  were  functionless 
and  dependent  on  the  activity  of  the  corresponding  ones  in  the 
maternal  organism. 

One  of  Harvey's  most  important  services  to  thought  lay  in  his 
abolishing  for  good  the  controversy  which  had  gone  on  ever  since 
the  sixth  century  B.C.  about  which  part  of  the  egg  was  for  nutrition 
and  which  for  formation.  He  had  the  sense  to  see  that  the  distinction 
was  a  useless  and  baseless  one — "There  is  no  distinct  part  (as  we 
have  often  said)  or  disposed  matter  out  of  which  the  Foetus  may  be 
formed  and  fashioned. .  .  .  An  egge  is  that  thing,  whose  liquors  do 
serve  both  for  the  Matter  and  the  Nourishment  of  the  foetus.. .  .Both 
liquors  are  the  nourishment  of  the  foetus." 

As  regards  spontaneous  generation,  Harvey  considered  that  even 
the  most  imperfect  and  lowest  animals  came  out  of  eggs.  "We  shall 
show",  he  writes,  "that  many  Animals  themselves,  especially  insects 
do  germinate  and  spring  from  seeds  and  principles  not  to  be  discerned 

148  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  11 

even  by  the  eye,  by  reason  of  their  contract  invisible  dimensions  (like 
those  Atomes,  that  fly  in  the  aire)  which  are  scattered  and  dispersed 
up  and  down  by  the  winds ;  all  which  are  esteemed  to  be  Spontaneous 
issues,  or  born  of  Putrefaction,  because  their  seed  is  not  anywhere 
seen."  Unfortunately,  he  never  returned  to  this  subject,  for,  as  he 
himself  informs  us  in  another  place,  all  the  papers  and  notes  in  his 
house  in  London  were  destroyed  at  the  time  of  the  Civil  War,  so  that 
what  he  had  written  on  the  generation  of  insects  irretrievably 

Another  point  on  which  Fabricius  had  been  in  error  was  the  ap- 
pearance of  bone  and  cartilage  in  the  embryo.  According  to  him, 
"Nature  first  stretcheth  out  the  Chine  Bone,  with  the  ribbes  drawn 
round  it,  as  the  Keel,  and  congruous  principle,  whereon  she  foundeth 
and  finisheth  the  whole  pile".  This  armchair  conceit  Harvey  was 
easily  able  to  destroy  by  a  mere  appeal  to  experience,  but  by  ex- 
perience also  he  came  upon  a  fact  less  easily  to  be  explained,  namely, 
that  the  motion  of  the  foetus  began  when  as  yet  there  was  hardly  any 
nervous  system.  "Nor  is  it  less  new  and  unheard  of,  that  there  should 
be  sense  and  motion  in  the  foetus,  before  his  brain  is  made;  for  the 
Foetus  moves,  contracts,  and  extends  himself,  when  there  is  nothing 
yet  appears  for  a  braine,  but  clear  water."  On  the  basis  of  this 
paradox  Harvey  may  be  said  to  be  the  discoverer  of  myogenic  con- 
traction, but  he  already  could  claim  that  distinction,  for  the  first 
heart-beats  are  accomplished  long  before  there  are  any  nerves  to  the 
heart,  as  he  himself  points  out.  "We  may  conclude  from  this  fact", 
he  remarks,  "that  the  heart  and  not  the  brain  is  the  first  principle 
of  embryonic  life",  and  he  gives  instances  of  physiological  actions 
not  under  the  conscious  control  of  the  individual,  such  as  the  reflexes, 
as  we  should  call  them,  of  the  intestinal  tract,  and  the  emetic  action 
of  infusion  of  antimony  which  cannot  be  tasted  much  and  "yet  there 
passeth  a  censure  upon  it  by  the  Stomack"  and  a  vomit  ensues.  Thus, 
twenty-five  years  before  Francis  Glisson,  Harvey  had  formulated, 
from  embryological  studies,  the  view  that  irritability  was  an  intrinsic 
property  of  living  tissues. 

Both  Harvey  and  Fabricius  were  very  puzzled  about  the  first 
origin  of  the  blood.  "What  artificer",  says  Harvey,  "can  transform 
the  two  liquors  into  blood,  when  there  is  yet  no  liver  in  being?" 
It  was  to  be  a  long  time  before  this  question  was  answered  by  Wolflf 's 
discovery  of  the  blood  islands  in  the  blastoderm,  and,  even  now,  the 


chemistry  of  the  appearance  of  haemoglobin  is  one  of  the  most  obscure 
corners  of  chemical  embryology.  The  older  observers  explained  it  by 
considering  the  yolk  to  be  akin  to  blood  and  ready  to  turn  into  it 
at  the  slightest  inducement. 

Another  problem  which  neither  Fabricius  nor  Harvey  did  any- 
thing to  solve  was  the  nature  of  the  air-space  at  the  blunt  end  of 
the  egg.  "Fabricius  recounts  several  conveniences  arising  from  it, 
according  to  its  several  magnitudes,  which  I  shall  declare  in  short, 
saying,  It  contains  aire  in  it,  and  is  therefore  commodious  to  the 
Ventilation  of  the  egge,  to  the  Respiration,  Transpiration,  and  Re- 
frigeration, and,  lastly,  to  the  Vociferation  of  the  Chicken.  Where- 
upon, that  cavity  is  at  the  first  very  little,  afterwards  greater,  and 
at  last  greatest  of  all,  according  as  the  several  recited  uses  do  require." 

As  regards  the  placenta,  Harvey  took  the  side  of  Arantius  and 
denied  any  connection  between  the  maternal  and  foetal  circulations. 
"The  extremities  of  the  umbilicall  vessels",  he  said,  "are  no  way 
conjoined  to  the  extremities  of  the  Uterine  vessels  by  an  Anastomosis, 
nor  do  extract  blood  from  them,  but  are  terminated  in  that  white 
mucilaginous  matter,  and  are  quite  obliterated  in  it,  attracting 
nourishment  from  it."  "Wherefore  these  caruncles  may  be  justly 
stiled  the  Uterine  Cakes  or  Dugs,  that  is  to  say,  convenient  and 
proportionate  organs  or  instruments  designed  for  the  concocting  of 
that  Albuginous  Aliment  and  for  preparing  it  for  the  attraction  of 
the  veins."  From  this  it  would  appear  that  Harvey  regarded  the 
uterine  milk  as  the  special  secretion  of  the  placenta,  conveyed  to  the 
foetus  through  the  umbilical  cord.  The  nature  of  the  uterine  milk 
is  still  very  imperfectly  understood  (see  Section  21).  Its  discovery  is 
usually  attributed  to  Walter  Needham,  but  various  remarks  in  this 
chapter  (Ex.  lxx)  seem  to  show  that  Harvey  was  well  acquainted 
with  it.  In  later  times,  it  was  regarded  by  some  (Bohnius  and 
Charleton  in  1686,  Zacchias  in  1688  and  Franc  in  1722)  as  the  sole 
source  of  foetal  nourishment.  Mercklin  spoke  of  it  in  1679  as  ''materia 
albuginea,  ovique  albo  non  absimili".  Harvey  often  calls  the  placenta 
the  uterine  liver,  no  doubt  only  for  this  reason,  but  the  remarkable 
appropriateness  of  the  term  was  to  become  apparent  in  Claude 
Bernard's  day.  As  regards  the  matter  of  the  continuity  of  the  maternal 
and  foetal  circulations,  he  criticises  van  Spieghel.  "There  came  forth 
a  book  of  late",  he  says,  "wrote  by  one  Adrianus  Spigelius,  wherein 
he  treateth  concerning  the  use  of  the  umbilicall  arteries  and  doth 

150  EMBRYOLOGY   IN  THE   SEVENTEENTH       [pt.  ii 

demonstrate  by  powerfull  arguments  that  the  Foetus  doth  not  receive 
its  Vital  Spirits  by  the  arteries  from  the  Mother,  and  hath  fully 
answered  those  arguments  which  are  alledged  to  the  contrary.  But 
he  might  also  as  well  have  proved  by  the  same  arguments  that  the 
blood  neither  is  transported  into  the  Foetus  from  the  mother's  veines 
by  the  propagations  of  the  umbilicall  veins  which  is  made  chiefly 
manifest  by  the  examples  drawn  from  the  Hen-Egge  and  the  Caesarean 

The  least  satisfactory  parts  of  Harvey's  book  are  the  Exercitations 
Lxxi  and  lxxii  on  the  innate  heat  and  the  primigenial  moisture. 
Here  he  becomes  very  wordy  and  highly  speculative,  and  gives  us 
little  but  a  mass  of  groundless  arguments.  He  devotes  many  pages 
to  proving  that  the  innate  heat  is  the  blood  and  to  drawing  distinc- 
tions between  blood  and  gore,  the  one  in  the  body,  the  other  shed. 
In  one  place  he  speaks  of  the  processes  of  generation  as  so  divine 
and  admirable  as  to  be  "beyond  the  comprehension  and  grasp  of 
our  thoughts  or  understanding".  Two  centuries  previously  Frasca- 
torius  had  said  precisely  the  same  thing  about  the  motion  of  the  heart, 
and  it  was  ironical  that  the  very  man  who  let  the  light  in  on  cardiac 
physiology  should  in  his  turn  despair  of  the  future  of  our  knowledge 
of  embryonic  development. 

Harvey  did  not  say  much  about  foetal  respiration,  and  his  few 
remarks  are  contained  in  one  of  the  "additional  discourses".  He  is 
puzzled  exceedingly  by  the  question.  But  he  comes  very  near  indeed 
to  the  truth  when  he  says,  "Whosoever  doth  carefully  consider  these 
things  and  look  narrowly  into  the  nature  of  aire,  will  (I  suppose) 
easily  grant,  that  the  Aire  is  allowed  to  animals,  neither  for  refrigera- 
tion, nor  nutrition  sake.  For  it  is  a  tryed  thing,  that  the  Foetus  is 
sooner  suffocated  after  he  hath  enjoyed  the  Aire,  than  when  he  was 
quite  excluded  from  it,  as  if  the  heat  within  him,  were  rather  inflamed 
than  quenched  by  the  aire".  Had  Harvey  pursued  this  line  of  thought, 
and  looked  still  more  narrowly  into  the  nature  of  air,  he  might  have 
anticipated  Mayow.  He  does  say  that  he  proposes  to  treat  of  the 
subject  again,  but  he  never  did. 

The  mainspring  of  Harvey's  researches  on  the  does  and  hinds  can 
be  realised  by  a  reference  to  Rueff's  figures  in  Fig.  6.  According 
to  the  Aristotelian  theory,  the  uterus  after  fertile  copulation  would 
be  full  of  blood  and  semen ;  according  to  the  Epicurean  theory  (held 
by  the  "physitians")  it  would  be  full  of  the  mixed  semina.    If  this 


coagulated  mass  exists,  said  Harvey,  it  ought  to  be  possible  to  find 
it  by  dissection,  and  this  was  what  he  tried  to  do.  It  soon  became 
plain,  as  may  be  read  in  Ex.  lxviii,  not  only  to  Harvey  but  to  the 
King  and  the  King's  gamekeepers,  that  no  such  coagulum  existed, 

^t^^^^^jr.    S>'^'^^^  ^>^T*-^^J-^     r    "^ 
^^^  A--r>  >^r'-/f  >^'^^  S"  ^,-^^  ^ ,  ■ 

x>  f.^^  ^^^^^/s  S^^  .  rr-  f 

Fig.  7.   Manuscript  notes  of  Dr  William  Harvey. 

and  the  result  was  made  still  more  certain  by  means  of  segregation 
experiments  which  the  King  carried  out  at  Hampton  Court.  Ac- 
cordingly there  was  nothing  to  be  done  but  to  abandon  all  the  older 
theories  completely,  and  have  recourse  to  some  sort  of  hypothesis 
in  which  an  aura  seminalis,  an  "incorporeal  agent"  or  a  "kinde 
of  contagious  property"  should  bring  about  fertilisation.  This  was 

152  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

a  perfectly  sound  deduction  from  Harvey's  experiments,  and  did  not 
then  appear  anything  like  so  unsatisfactory  as  it  does  now,  for  Gilbert 
of  Colchester  was  not  long  dead,  the  "lodestone"  was  beginning 
to  be  investigated  by  the  virtuosi,  and  even  such  extravagances  as 
Sir  Gilbert  Talbot's  Powder  "for  the  sympatheticall  cure  of  wounds" 
were  only  with  difficulty  distinguishable  from  the  real  effects  of 
magnetic  force.  Harvey's  idea  of  fertilisation  by  contagion  has  recently 
been  in  a  sense  revived  by  the  work  of  Shearer  (see  Section  4*2). 

But  to  Harvey  himself  the  subject  of  the  action  of  the  seed  was 
hid  in  deep  night,  and  he  confessed  that,  when  he  came  to  it,  he 
was  "at  a  stand".  Some  very  interesting  light  is  thrown  upon  his 
mind  in  this  connection  by  a  copy  of  the  De  Generatione  Animalium 
annotated  by  himself,  and  now  in  the  possession  of  Dr  Pybus,  by 
whose  courtesy  and  by  that  of  Dr  Singer,  who  has  transcribed  the 
notes,  I  have  been  enabled  to  study  it.  It  was  given  by  Harvey  to 
his  brother  Eliab,  whose  name  it  still  bears.  The  notes,  which  are 
on  the  fly-leaves,  are  written  in  much  the  same  way  as  those  famous 
ones  which  Harvey  used  for  his  lectures  at  the  College  of  Physicians  in 
London,  and  which  have  been  reproduced  in  facsimile.  There  is  the 
same  mixture  of  Latin  and  English,  and  the  same  signs,  such  as  WI,  to 
denote  thoughts  claimed  as  original.   A  page  is  reproduced  in  Fig.  7. 

For  the  most  part,  the  notes  are  uninteresting  and  nothing  but  a 
confusion  of  Aristotelian  terms.  But  one  page  is  concerned  with  the 
mode  of  action  of  the  seed,  and  here  we  can,  as  it  were,  see  Harvey's 
mind  wrestling  with  this  most  difficult  of  problems.  He  sees  that 
odour  and  the  sense  of  smell  may  give  a  clue.  That  his  thoughts  on 
this  point  were  doomed  to  frustration  as  soon  as  eggs  and  spermatozoa 
were  discovered  does  not  detract  from  the  interest  of  the  struggle. 

Quod  facit  semen  fecundum 

What  makes  the  seed  fertile  is  on  the  analogy  of  an  injection.  In  fact, 
the  injection  causes  disease  in  many  cases,  and  that  from  a  distance,  both 
by  another. .  .and  by  the  same. .  .  A  Venereal  (?)  disease  corrupts  coitus 
with  a  woman  in  whose  uterus  is  the  poison. 

They  do  not  [or  do  not  yet  ?]  come  forth  in  actuality  but  lie  dormant 
as  in  fuel  [?  fomite].  Again,  rabies  in  dogs  lies  dormant  for  many  days 
on  my  own  observation  W4.  Again,  smallpox  for  days.  Again,  the  genera- 
tive seed,  just  as  it  (passes)  from  the  male,  lies  dormant  in  the  woman  as 

Or  else  like  a . . . ,  like  light  in  stone . .  . ,  the  pupil  in  the  eye,  in  sense 
motion, ...  in  the  body. 


Like  ferment,  vapour,  odour,  rottenness ...  by  rule. 
Or  like  the  smell  given  off  by  flowers. 

Like  heat,  inflammation  (?)    A  in  chalk  (heat  ?)  both  the  wet  form 

Like  what  is  first ...  in  the  art  of  cooking .  .  .  principles  of  vegetation  and 
propagation.  A  Dormice  by  hibernating.  .  .cleansing  by  water  and  all 
kinds  of  lotions,  again  for  insects,  as  for  their  seeds  as  well  (?).  Or  when 
a  soul  is  a  god  present  in  nature,  that  is  divine  which  it  brings  about 
without  an  organic  body  by  means  of  law. 

See  Aristode  Marvels  concerning  odours  and  smells  given  off.  Whether 
on  sense  and  everything  that  can  be  smelt  gives  off  something  and  so 
the  objects  of  disperses  (?)  what  is  not  without  heat,  or  by  destroying .  .  . 
sense.  attracts  to  itself 

A  Amongst  inflammable  (objects  are)  fire,  naphtha,  paper 

A  WI  manus  et  odore  car . .  .  anatomia  manair. ... 

A  Anat .  .  .  post  4°"^  poras.  otium  inclinente  die  rursus  quod  prius  et 

olefrere  vid. . .  .  Galen. ... 
A  Mr.  Boys  spainel  in  Paris  lay  all  ye  third  night  and  morning  in 
getting  dogg.  Whelping  dogg's  sent  (scent)  are  a  stronger  sent, 
vesting  in  vestigio  alios  ord .  .  .  gr .  .  .  lepris  odore  lepris  esse 
libidine  esse.  Hors,  the  mare,  hors,  the  cow,  a  bull  per  mutta 
A  ...  si  lepra  fracedo  in  farioli  fader  cupidinitus.  Dogg  ye  otter  in  aquas 
fracedo  vasorum  ex  sulpore? 

Just  as  Aristotle  put  much  of  his  best  embryological  work  into  his 
Historia  Animalium  and  not  into  the  work  with  the  appropriate  title, 
so  Harvey  has  some  admirable  observations  on  the  embryonic  heart 
scattered  through  his  De  Motu  Cordis  et  Sanguinis  in  Animalibus.  Turning 
now  to  consider  Harvey's  influence  on  embryology,  we  must  admit 
that  it  was  in  certain  respects  reactionary. 

1 .  He  did  not  break  with  Aristotelianism,  as  a  few  of  his  pre- 
decessors had  already  done,  but  on  the  contrary  lent  his  authority 
to  a  moribund  outlook  which  involved  the  laborious  treatment  of 
unprofitable  questions. 

2.  His  opposition  to  atomism  and  to  "chymistry"  precluded  any 
close  co-operation  between  his  followers  and  those  of  the  Descartes- 
Gassendi  tradition. 

3.  Fabricius  had  elaborated  a  vitalistic  theory  of  differentiation, 
but  had  allowed  growth  to  be  "natural"  or  mechanical.  Harvey, 
however,  made  both  growth  and  differentiation  the  results  of  an 
immanent  spirit,  a  sort  of  divine  legate. 

But  these  failings  are  far  outweighed  by  his  positive  services.  It 
must  always  be  remembered  that  he  had  no  compound  microscope. 

154  EMBRYOLOGY   IN  THE   SEVENTEENTH       [pt.  ii 

and  had  to  rely,  like  Riolanus,  on  "perspectives",  or  simple  lenses 
of  very  low  power. 

1.  There  can  be  no  doubt  that  the  doctrine  omne  vivum  ex  ovo 
was  a  tremendous  advance  on  all  preceding  thought.  Harvey's 
scepticism  about  spontaneous  generation  antedated  by  less  than  a 
century  the  experiments  of  Redi.  It  is  important  to  note  that  he  was 
led  to  his  idea  of  the  mammalian  ovum  by  observations  on  small 
conceptions  surrounded  by  their  chorion  and  no  bigger  than  eggs, 
for  the  true  ovum  itself  was  not  discovered  until  the  time  of  de  Graaf 
and  Stensen. 

2.  He  identified  definitely  and  finally  the  cicatricula  on  the  yolk- 
membrane  as  the  spot  from  which  the  embryo  originated. 

3.  He  denied  the  possibility  of  generation  from  excrement  and 
from  mud,  saying  that  even  vermiparous  animals  had  eggs. 

4.  He  discussed  the  question  of  metamorphosis  (preformation)  and 
epigenesis,  and  decided  plainly  for  the  latter,  at  any  rate  for  the 
sanguineous  animals. 

In  addition  to  these  achievements,  there  are  others,  perhaps  less 
striking,  but  equally  important. 

5.  He  destroyed  once  and  for  all  the  Aristotelian  (semen-blood) 
and  Epicurean  (semen-semen)  theories  of  early  embryogeny.  This 
was  perhaps  the  biggest  crack  he  made  in  the  Peripatetic  teaching 
on  development;  but,  in  spite  of  it,  Sennertus,  van  Linde  and 
Sylvius  adhered  to  the  ancient  views,  and  Cyprianus,  in  1700, 
had  the  distinction  of  being  the  last  to  support  them  in  a  scientific 
discussion,  though  Sterne,  as  late  as  1 759,  referred  to  them  in  a  way 
that  shows  they  still  lived  on  in  popular  thought. 

6.  He  handled  the  question  of  growth  and  differentiation  better 
than  any  before,  anticipating  the  ideas  of  the  present  century. 

7.  He  settled  for  good  the  controversy  which  had  lasted  for  2200 
years  as  to  which  part  of  the  egg  was  nutritive  and  which  was  forma- 
tive, by  demonstrating  the  unreality  of  the  distinction. 

8.  He  set  his  predecessors  right  on  a  very  large  number  of  detailed 
points,  such  as  the  nature  of  the  placenta. 

9.  He  made  a  great  step  forward  in  his  theory  of  foetal  respiration, 
though  here  he  did  not  consolidate  the  gain. 

10.  He  affirmed  that  embryonic  organs  were  active,  and  that  the 
embryo  did  not  depend  on  external  aid  for  its  principal  physiological 


But  all  these  titles  to  remembrance,  great  as  they  are,  do  not 
account  for  the  pecuhar  fascination  of  Harvey.  A  little  of  it  is  perhaps 
due  to  his  imaginative  style,  which  comes  out  clearly  in  Martm 
Llewellyn's  English  version.  A  word  of  censure  is  due  to  Willis 
for  transmuting  it  in  his  translation  into  the  dull  and  pedestrian 
style  of  1847.  None  who  reads  the  1653  edition  of  Harvey  can  ever 
forget  such  metaphors  as  this,  "For  the  trunck  of  the  body  hitherto 
resembles  a  skiff  without  a  deck,  being  in  no  way  covered  up  by 
the  anteriour  parts";  or  the  vigour  of  diction  which  promotes  such 
remarks  as,  "In  a  hen-egge  after  the  tenth  day,  the  heart  admits  no 
spectators  without  dissection";  or  again,  "For  while  the  foetus  is  yet 
feeble.  Nature  hath  provided  it  milder  diet  and  solider  meats  for  its 
stronger  capacity,  and  when  it  is  now  hearty  enough,  and  can  away 
with  courser  cates,  it  is  served  with  commons  answerable  to  it.  And 
hereupon  I  conceive  that  perfect  eggs  are  not  onely  party-coloured, 
but  also  furnished  with  a  double  white";  or,  lastly,  "An  egge  is,  as  it 
were,  an  exposed  womb ;  wherein  there  is  a  substance  concluded,  as 
the  Representative  and  Substitute  or  Vicar  of  the  breasts". 

In  this  connection,  it  would  be  a  pity  not  to  quote  from  the  verses 
which  Llewellyn  prefixed  to  his  translation  of  Harvey's  book.  After 
describing  the  controversies  that  followed  the  De  Motu  Cordis  he  wrote 

A  Calmer  Welcome  this  choice  Peice  befall, 

Which  from  fresh  Extract  hath  deduced  all, 

And  for  Belief,  bids  it  no  longer  begg 

That  Castor  once  and  Pollux  were  an  Egge : 

That  both  the  Hen  and  Houswife  are  so  matcht, 

That  her  Son  born,  is  only  her  Son  hatcht; 

That  when  her  Teeming  hopes  have  prosp'rous  bin. 

Yet  to  conceive,  is  but  to  lay,  within. 

Experiment,  and  Truth  both  take  thy  part: 

If  thou  canst  'scape  the  Women !  there's  the  Art. 

Live  Modern  Wonder,  and  be  read  alone, 

Thy  Brain  hath  Issue,  though  thy  Loins  have  none. 

Let  fraile  Succession  be  the  Vulgar  Care; 

Great  Generation's  Selfe  is  now  thy  Heire. 

Curiously  enough,  the  "calmer  welcome"  which  Martin  Llewellyn 
hoped  for  actually  happened.  Harvey's  book  was  so  well  reasoned 
and  based  on  such  good  observations  that  it  produced  only  two 

156  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  11 

answers,  and  they  were  of  little  importance.  Janus  Orcham  took 
exception  to  Harvey's  finding  no  seed  in  the  uterus  and  suggested 
that  it  had  vaporised  like  a  steam,  but  his  Aristotelian  leanings  were 
promptly  detected  and  castigated  by  Rallius.  Matthew  Slade,  taking 
the  pseudonym  of  Theodore  Aides,  published  in  1667  his  Dissertatio 
epistolica  contra  D.  G.  Harveium,  which  was,  in  his  own  words,  "a 
detection  of  one  or  two  errors  in  that  golden  book  on  the  generation 
of  animals  of  William  Harvey,  greatest  of  physicians  and  anatomists". 
The  errors  were  purely  anatomical,  and  ab  Angelis  defended  Harvey 
against  Slade's  attack,  claiming  that  the  "errors"  were  not  errors 
at  all.   A  manuscript  work  of  Slade's  appears  to  be  extant. 

Harvey's  influence  was  evidently  speedily  felt  by  his  contemporaries. 
Strauss  soon  wrote  a  rather  poor  book  on  the  bird's  egg  in  imitation 
of  him.  But  the  best  instance  is  that  in  1655,  very  soon  after  the 
publication  of  Harvey's  book,  William  Langly,  "an  eminent  senator 
and  physician  of  Dordrecht",  made  a  great  many  experiments  on 
the  development  of  the  hen's  egg.  Buffon  says  that  he  worked  in 
1635,  i.e.  before  Harvey,  but  this  is  not  the  case,  for  in  his  observa- 
tions which  were  published  by  Julius  Schrader  in  1674  the  later  date 
is  given  several  times.  Langly  mentions  Harvey  more  than  once, 
and  evidently  followed  his  example  in  careful  observation,  for  his 
text  is  concise  and  accurate  and  his  drawings  very  noteworthy. 

Julius  Schrader  included  Langly's  work  in  a  composite  volume 
containing  a  well-arranged  epitome  of  Harvey's  book  on  generation 
and  some  observations  of  his  own  on  the  hen's  egg.  The  book  was 
dedicated  to  Matthew  Slade  and  J.  Swammerdam.  On  the  practical 
side  Schrader  added  nothing  memorable  to  Harvey  and  Langly,  but 
it  is  noteworthy  that  the  mammalian  embryo  was  throughout  these 
centuries  more  popular  material  than  that  of  the  chick.  Out  of  fifty 
embryologists  between  Harvey  and  Haller,  the  names  of  Langly, 
Schrader,  Malpighi  and  Maitre-Jan  practically  exhaust  the  list  of 
those  who  studied  the  egg  of  the  hen.  This  rather  unfortunate  orienta- 
tion of  mind  doubtless  sprang  from  the  strong  influence  of  medicine, 
and  especially  obstetrics,  on  seventeenth  and  eighteenth  century 

3-5.    Gassendi  and  Descartes:  Atomistic  Embryology 

Harvey's  death  took  place  in  1657.  The  following  year  saw  the 
publication  of  Pierre  Gassendi's  Opera  Omnia,  and  thus  brought  in 


an  entirely  new  phase  in  embryology.  Together  with  Rene  Descartes' 
treatise  on  the  formation  of  the  foetus,  Gassendi's  De  generatione 
animalium  et  de  animatione  foetus  marks  a  quite  different  attitude  to  the 
subject.  Harvey  had  adopted  a  rather  contemptuous  position  about 
the  "corpuscularian  or  mechanical  philosophy",  which  was  then 
coming  in,  and  had  expected  even  less  help  from  it  in  the  solution 
of  his  problems  than  from  his  equally  despised  "chymists".  Gassendi 
now  set  out  to  show  that  the  formation  of  the  foetus  could  be  explained 
on  an  atomistic  basis:  and,  using  the  Galenic  physiology  and  the 
new  anatomy  as  a  framework,  he  set  forth  his  theory  in  full.  As  we 
read  it  through  at  the  present  day,  however,  we  cannot  avoid  the 
confession  that  it  was  not  a  success.  In  spite  of  his  frequent 
quotations  from  Lucretius  and  his  persuasive  style,  it  does  not 
carry  conviction.  The  truth  of  the  matter  was  that  the  time  was 
not  ripe  for  so  great  a  simplification.  The  facts  were  insufficiently 
known,  and  that  Gassendi  is  not  quite  as  interested  in  them  as  he  is 
in  his  theory  is  shown  by  the  circumstance  that  he  only  mentions 
Harvey  once. 

Gassendi  examines  in  turn  the  Aristotelian  and  the  Epicurean 
doctrines  of  embryogeny  and  rejects  them  both,  the  former  on  the 
ground  that  the  change  from  tgg  to  hen  is  too  great  and  difficult 
for  anything  so  shadowy  and  ghost-like  as  a  "form"  to  accomplish, 
and  the  latter  because  it  leaves  no  room  for  teleology.  He  therefore 
adopts  as  the  basis  of  his  system  atomism  +  preformationism,  al- 
leging that  all  the  germs  of  living  things  were  made  at  the  creation, 
but  that  they  come  to  their  perfection  as  atomic  congregations  in  an 
atomistic  universe.  Thomas'  monograph  is  a  valuable  help  to  the 
study  of  this  very  interesting  thinker. 

At  exactly  the  same  time,  Descartes  was  speculating  on  the  same 
subject.  Added  to  his  posthumous  De  Homine  Liber  (1662)  is  a  treatise 
on  the  formation  of  the  foetus.  He  may  also  have  written  a  work 
On  the  generation  of  animals,  for  a  manuscript  with  that  title  was  found 
among  his  papers  after  his  death,  and  was  believed  to  be  in  his 
handwriting.  There  is  evidence,  however,  that  it  is  not  his,  and  though 
it  was  published  in  Cousin's  edition  of  his  works,  we  may  safely 
neglect  it,  agreeing,  in  the  words  of  that  editor,  that  it  is  "a  fragment 
in  which  very  mediocre  and  often  quite  false  ideas  struggle  to  light 
through  the  medium  of  a  style  devoid  alike  of  clarity  and  of  grandeur  ". 
It  must  be  admitted,  however,  that  even  his  main  treatise  is  very 

158  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  11 

confused.  It  suffers  from  containing  in  its  earlier  part  a  great  deal 
of  matter  which  really  belongs  to  the  physiological  text-book  which 
immediately  preceded  it.  Thus  it  begins  abruptly  in  the  middle  of 
a  disquisition  on  the  error  of  attributing  bodily  functions  to  the  soul. 
Before  long,  however,  it  warms  to  its  theme,  and  a  conception  of 
growth  is  outlined.  "When  one  is  young,  the  movement  of  the  little 
threads  which  compose  the  body  is  less  slow  than  it  is  in  old  age, 
because  the  threads  are  not  so  tightly  joined  one  to  the  other,  and 
the  streams  in  which  the  solid  particles  run  are  large,  so  that  the 
threads  become  attached  to  more  matter  at  their  roots  than  detaches 
itself  from  their  extremities,  so  that  they  grow  longer  and  thicker, 
in  this  way  producing  growth."  The  fourth  part  of  the  book  is  called, 
strangely  enough,  a  Digression,  in  which  the  formation  of  the  animal 
is  spoken  of.  The  mixture  of  seeds  is  then  described,  and  a  theory 
of  the  formation  of  the  heart  is  attempted  by  means  of  an  analogy 
with  fermentation.  The  explanation  is  unconvincing,  but  has  a  cer- 
tain interest  as  showing  chemical  notions  beginning  to  permeate 
biological  thought.  However,  Descartes'  way  of  looking  at  develop- 
ment was  thoroughly  novel,  as  is  illustrated  by  the  following  citation. 
"How  the  heart  begins  to  move.. .  .Then,  because  the  little  parts 
thus  dilated,  tend  to  continue  their  movement  in  a  straight  line,  and 
because  the  heart  now  formed  resists  them,  they  move  away  from  it 
and  take  their  course  towards  the  place  where  afterwards  the  base 
of  the  brain  will  be  formed,  they  enter  into  the  place  of  those  that 
were  there  before,  which  for  their  part  move  in  a  circular  manner 
to  the  heart  and  there,  after  waiting  for  a  moment  to  assemble 
themselves,  they  dilate  and  follow  the  same  road  as  the  aforemen- 
tioned ones,  etc."  Descartes,  in  fact,  with  premature  simplification, 
was  trying  to  erect  an  embryology  more  geometrico  demonstrata. 
That  he  failed  in  the  attempt  was  as  obvious  to  his  contemporaries 
as  it  is  to  us — "We  see",  said  Garden,  "how  wretchedly  Descartes 
came  off"  when  he  began  to  apply  the  laws  of  motion  to  the  forming 
of  an  animal".  In  doing  so,  he  was  many  years  before  his  time; 
Borelli  had  done  all  that  could  be  done  at  that  period  in  that  direc- 
tion, and,  significantly  enough,  he  left  embryology  alone.  The  rest 
of  Descartes'  book  is  exactly  like  the  citations  which  have  been  given, 
only  applied  to  each  organ  and  part  in  turn;  he  practically  uses  the 
traditional  teaching  as  a  scaffolding  in  which  to  interweave  his 
mechanical  theory,  and  he  discovers  no  new  facts. 


But  in  the  history  of  embryology  these  men  and  their  writings  have 
a  very  great  significance.  Impressed  by  the  unity  of  the  world  of 
phenomena,  they  wished  to  derive  embryology  as  well  as  physics 
from  fundamental  laws.  This  attempt,  which  resulted  in  a  Galen- 
Epicurus  synthesis  on  the  one  hand  and  a  Galen-Descartes  synthesis 
on  the  other,  must  be  regarded  as  a  noble  failure.  Its  authors  did  not 
realise  what  a  vast  array  of  facts  would  have  to  be  discovered  before 
a  mechanical  theory  could  with  any  justice  be  applied  to  explain 
them.  Gassendi  and  Descartes  were  like  the  Ionian  nature-philo- 
sophers, propounding  general  laws  before  the  particular  instances 
were  accurately  known.  Their  ineffectiveness  arises  from  the  fact 
that  they  did  not  themselves  appreciate  this,  and  consequently 
worked  out  their  idea  in  a  prolix  detail,  the  whole  of  which  was 
inevitably  doomed  to  the  scrap-heap  from  the  very  beginning.  But 
the  spark  was  not  to  die ;  and  if  anywhere  in  this  history  we  are  to 
find  the  roots  of  physico-chemical  embryology,  we  must  pause  to 
recognise  them  here. 

Much  less  well  known,  but  not  without  interest,  was  the  Dissertatio 
de  vita  foetus  in  utero  of  Gregorius  Nymmanus,  which  appeared  in  the 
same  year  as  the  second  edition  of  Descartes'  book,  1664.  Nymmanus 
writes  with  a  very  beautiful  Latin  style,  and  expresses  himself  with 
great  clearness.  His  proposition  is,  he  says,  "That  the  foetus  in  the 
uterus  lives  with  a  life  of  its  own  evincing  its  own  vital  actions,  and 
if  the  mother  dies,  it  not  uncommonly  survives  for  a  certain  period, 
so  that  it  can  sometimes  be  taken  alive  from  the  dead  body  of  its 
mother".  In  supporting  this  thesis,  Nymmanus  answers  the  argu- 
ments of  those  who  had  held  that  the  lungs  and  heart  of  the  foetus 
were  inactive  in  utero.  Fabricius,  Riolanus  and  Spigelius  all  proved, 
says  Nymmanus,  that  the  mother  and  the  foetus  by  no  means  neces- 
sarily die  at  the  same  time.  "The  essential  life",  he  says,  "is  the  soul 
itself  informing  and  activating  the  body,  the  accidental  life  is  the  acts 
of  the  soul  which  it  performs  in  and  with  the  body."  Though  the 
foetus  cannot  be  said  to  have  life  in  the  latter  sense,  it  can  in  the 
former.  The  foetus,  says  Nymmanus,  prepares  its  own  vital  spirits 
and  the  instruments  of  its  own  soul;  there  is  no  nerve  between  it  and 
its  mother.  If,  he  says,  the  foetal  arteries  got  their  sphygmic  power 
from  the  maternal  heart,  they  would  stop  pulsating  when  the  umbilical 
cord  was  tied,  but  this  is  not  the  case.  The  pulse  of  the  embryo  is 
therefore  due  to  the  foetal  heart  itself.   Galen,  says  Nymmanus,  was 

i6o  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

aware  of  this,  but  did  not  understand  the  meaning  of  it.  Again,  the 
foetus  in  utero  moves  during  the  mother's  sleep,  and  vice  versa.  Nym- 
manus'  dissertation  is  an  interesting  study  in  the  transition  from 
theological  to  scientific  embryology  which  took  place  all  through  the 
seventeenth  century,  and  may  be  followed  in  the  writings  of  Varan- 
daeus,  de  Castro,  Dolaeus,  Hildanus,  Scultetus,  Ammanus,  Augerius 
and  Garmannus.  The  problem  of  animation-time,  a  more  meta- 
physical aspect  of  the  same  question,  was  still  being  handled,  but 
less  attention  was  being  paid  to  it  than  formerly.  Honoratus  Faber's 
De  Generatione  Animalium  of  1666  does  not  belong  to  its  period.  Its 
author,  a  Jesuit,  proceeds  in  scholastic  fashion  to  lay  down  four 
definitions,  three  axioms,  one  hypothesis,  and  seventy-seven  pro- 
positions, in  the  last  of  which  he  summarises  his  conclusions.  He  is 
interesting  in  that  he  displayed  a  disbelief  in  spontaneous  generation, 
thereby  anticipating  Redi,  and  he  is  careful  to  mention  the  work  of 
Harvey,  but  nevertheless  his  treatise  is  of  little  value.  His  chief 
importance  is  that  he  is  an  epigenesist,  and  therefore  demonstrates 
to  us  how  the  true  opinion  was  becoming  accepted,  when  Malpighi's 
brilliant  observations  and  bad  theory  sent  it  out  of  favour,  and  pre- 
pared the  way  for  the  numerous  controversies  of  the  following 

3-6.    Walter  Needham  and  Robert  Boyle 

It  was  in  1666  also  that  the  following  appeared  in  the  Philosophical 
Transactions  of  the  Royal  Society : 

A  way  of  preserving  birds  taken  out  of  the  egge,  and  other  small  f actus' s: 
communicated  by  Mr.  Boyle. 

When  I  was  sollicitous  to  observe  the  Processe  of  Nature  in  the  Forma- 
tion of  the  Chick,  I  did  open  Hens  Eggs,  some  at  such  a  day,  and  some 
at  other  daies  after  the  beginning  of  the  Incubation,  and  carefully  taking 
out  the  Embryo's,  embalmed  each  of  them  in  a  distinct  Glass  (which  is 
to  be  carefully  stopt)  in  Spirit  of  Wine;  Which  I  did,  that  so  I  might  have 
them  in  readinesse  to  make  on  them,  at  any  time,  the  Observations,  I 
thought  them  capable  of  affording;  and  to  let  my  Friends  at  other  seasons 
of  the  year,  see,  both  the  differing  appearances  of  the  chick  at  the  third, 
fourth,  seventh,  fourteenth,  or  other  daies,  after  the  eggs  had  been  sate 
on,  and  (especially)  some  particulars  not  obvious  in  chickens,  that  go 
about,  as  the  hanging  of  the  Gutts  out  of  the  Abdomen,  etc.    How  long 

sfecT.  3]  AND   EIGHTEENTH   CENTURIES  161 

the  tender  Embryo  of  the  Chick  soon  after  the  Punctum  saliens  is 
discoverable,  and  whilst  the  bodie  seems  but  a  little  organized  Gelly, 
and  some  while  after  that,  will  be  this  way  preserv'd,  without  being 
too  much  shrivel'd  up,  I  was  hindred  by  some  mischances  to  satisfie 
myself;  but  when  the  Faetus's,  I  took  out,  were  so  perfectly  formed 
as  they  were  wont  to  be  about  the  seventh  day,  and  after,  they  so 
well  retained  thjeir  shape  and  bulk,  as  to  make  me  not  repent  of  my 
curiosity;  And  some  of  those,  which  I  did  very  early  this  Spring,  I  can 
yet  shew  you. 

Boyle  said  in  conclusion  that  he  sometimes  also  "added  Sal 
Armoniack,  abounding  in  a  salt  not  sowre  but  urinous". 

In  the  same  year  that  Nymmanus'  book  appeared,  Nicholas 
Stensen,  that  great  anatomist,  later  a  Bishop,  who  was  also  to  all 
intents  and  purposes  the  founder  of  geology,  published  his  De  musculis 
et  glandulis  specimen,  in  which  Goiter's  observations  on  the  vitelline 
duct  and  the  general  relations  between  embryo  and  yolk  in  the  hen's 
tgg  were  made  again  and  confirmed.  About  this  time  also  Deusingius 
described  his  case  of  abdominal  pregnancy,  and  was  thus  the  first 
anatomist  to  draw  attention  to  this  phenomenon. 

In  1667  Stensen  published  his  Elementorum  myologiae  specimen,  in 
which  he  described  the  female  genital  organs  of  dogfishes.  He 
demonstrated  eggs  in  them  and  affirmed  that  the  "testis"  of  women 
ought  to  be  regarded  as  exactly  the  same  organ  as  the  "ovary"  or 
"roe"  of  ovipara.  At  the  time  he  carried  the  suggestion  no  further, 
but  it  was  an  extremely  fruitful  one,  and  it  is  surprising  that  it  did 
not  create  more  interest,  for  it  was  exactly  what  Harvey  had  been 
looking  for.  Nothing  obvious  having  been  found  in  the  uteri  of  King 
Charles'  does,  and  the  conviction  yet  being  very  strong  that  viviparous 
conceptions  really  came  from  eggs,  Stensen's  minute  ova  supplied 
the  fitting  answer  to  the  question.  Thus  Harvey  and  Stensen  between 
them  substituted  the  modern  knowledge  of  mammalian  ova  for  the 
ancient  theory  of  the  coagulum  all  in  the  space  of  fourteen  years.  The 
other  event  for  which  the  year  1667  is  remarkable  is  the  De  Formato 
Foetu  of  Walter  Needham.  Needham  was  a  Cambridge  physician 
who  went  to  Oxford  to  study  in  the  active  school  of  physiological 
research  which  such  men  as  Christopher  Wren,  Richard  Lower,  John 
Ward  and  Thomas  Willis  were  making  famous.  His  book  on  the 
formation  of  the  embryo,  written  later  (and  dedicated  to  Robert 
Boyle),  after  he  had  been  in  practice  in  Shropshire  for  some  time. 

i62  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

is  important  because  it  is  the  first  book  in  which  definite  chemical 
experiments  on  the  developing  embryo  are  reported,  and  also 
because  it  contains  the  first  practical  instructions  for  dissections  of 

Sir  Thomas  Browne  had,  as  we  have  already  seen,  made  experi- 
ments of  a  chemical  nature  on  the  constituents  of  birds'  eggs  and  of 
the  eggs  of  amphibia,  but  he  did  not  analyse  them  after  any  develop- 
ment had  been  allowed  to  take  place.  He  may  therefore  be  regarded 
as  the  father  of  the  static  aspect  of  physico-chemical  embryology, 
while  Walter  Needham  may  be  regarded  as  the  founder  of  the 
dynamic  aspect.  The  practical  difficulties  of  these  pioneers  of  animal 
chemistry  may  be  seen  in  such  a  book  of  practical  instructions  as 
Salmon's  General  Practise  ofChymistry  of  1678.  They  had  no  satisfactory 
glassware,  no  pure  reagents,  the  methods  of  heating  were  incredibly 
clumsy,  and  there  was  no  means  of  measuring  either  heat  or  atmo- 
spheric pressure. 

In  the  review  of  Needham's  book  which  is  to  be  found  in  the 
Philosophical  Transactions  of  the  Royal  Society  for  September  1667  there 
occurs  the  sentence,  "These  humors  (the  amniotic,  allantoic,  etc.) 
he  saith,  he  hath  examined,  by  concreting,  distilling,  and  coagulating 
them;  where  he  furnishes  the  Reader  with  no  vulgar  observations". 
What  were  these  observations  ?  They  are  to  be  found  in  the  chapter 
entitled  "The  nature  of  the  humours": 

"I  now  proceed  to  speak  of  this  other  nutritive  liquor  round  about 
the  urine  itself  which  latter  is  plainly  separated  by  the  kidneys  and 
the  bladder.  These  liquors  also  proceed  from  the  blood  and  seem 
similar  to  its  serum  but  yet  they  are  different  from  it.  For  when  fire 
is  applied  to  them  in  an  evaporating  basin  [cochlea]  they  do  not 
coagulate,  as  the  blood-serum  always  does.  Indeed,  not  even  the 
colliquamentous  liquid  of  the  egg  itself  coagulates  in  this  manner, 
although  it  is  formed  from  juices  which  are  evidently  liable  to  coagu- 
lation— in  the  same  way  humours  differ  from  themselves  before  and 
after  digestion,  filtration,  and  the  other  operations  [mangonial  of 
nature.  All,  when  distilled,  give  over  a  soft  and  clear  water  [mollem 
et  lenem]  very  like  distilled  milk.  This  property  is  common  to  the  liquor 
of  the  allantoic  space,  along  with  the  rest.  Because  when  the  salts 
are  not  yet  made  wild  and  exalted  the  serum  of  the  blood  remains 
still  quite  soft  and  does  not  give  proof  of  a  tartaric  or  saline  nature. 
Indeed,  the  first  urine  of  an  infant  is  observed  by  nurses  to  be  not  at 


all  salt,  but  in  older  animals,  when  I  distilled  it  in  an  alembic,  I 
seemed  to  observe  a  little  volatile  salt  at  the  small  end  [in  capitello]. 
Coagulations  attempted  by  acids  happened  differently  in  respect  of 
the  different  humours.  For  when  I  poured  a  decoction  of  alumina 
into  the  liquor  of  the  cow's  amnios  it  exhibited  a  few  rather  fine 
coagulations  but  they  were  clearly  white.  The  allantoic  juice,  how- 
ever, was  precipitated  like  urine.  Spirits  of  vitriol  and  vinegar 
brought  about  less  results  than  alumina  in  each  case.  Spontaneous 
concretions  I  found  also  in  the  later  months;  these  I  discovered  in 
both  places.  They  are  more  frequent  and  larger,  however,  within 
the  allantoic  membrane." 

From  the  above  excerpt,  which  contains  the  account  of  all  that 
Needham  did  on  the  chemical  composition  of  the  embryonic  liquids, 
it  can  be  seen  that  he  treated  the  whole  matter  more  dynamically 
than  Browne.  He  was  the  first  to  describe  the  solid  bodies  in  the 
amniotic  fluid  (see  Jenkinson)  and  his  chemical  experimentation  was 
all  pioneer  work. 

His  book  has  other  merits,  however.  In  the  first  chapter,  he  refutes 
the  theory  which  Everard  had  propounded,  that  the  uterine  milk  was 
identical  with  the  contents  of  the  thoracic  duct,  conveyed  by  lym- 
phatic vessels  to  the  uterus  from  the  lac  teals  of  Aselli,  instead  of 
elsewhere,  and  he  shows  that  arteries  must  be  the  vessels  bringing 
the  material  to  the  womb.  The  second  chapter  deals  with  the  placenta 
"where  he  giveth  a  particular  account  of  the  double  Placenta  or 
Cake,  to  be  found  in  Rabbets,  Hares,  Mice,  Moles,  etc.,  and  examines 
the  learned  Dr  Wharton's  doctrine,  assigning  a  double  placenta  to  at 
least  all  the  viviparous  animals,  so  as  one  half  of  it  belongs  to  the 
Uterus,  the  other  to  the  Chorion,  shewing  how  far  this  is  true,  and 
declaring  the  variety  of  these  Phaenomena.  Where  do  occur  many 
uncommon  observations  concerning  the  difference  of  Milk  [uterine] 
in  ruminating  and  other  animals,  the  various  degrees  of  thickness  of 
the  uterin  liquor  in  oviparous  and  viviparous  creatures".  He  de- 
scribes the  human  placenta  very  correctly  indeed.  "The  use  of  the 
placenta  is  known  to  be  to  serve  for  conveighing  the  aliment  to  the 
foetus.  The  difficulty  is  only  about  the  manner.  Here  are  examined 
three  opinions,  of  Curvey,  Everhard,  and  Harvey.  The  two  former 
do  hold  that  the  foetus  is  nourished  only  from  the  Amnion  by  the 
mouth ;  yet  with  this  difference,  that  Curvey  will  have  it  fed  by  the 
mouth  when  it  is  perfect,  but  whilst  it  is  yet  imperfect,  by  filtration 

i64  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

through  all  the  pores  of  the  body,  and  by  a  kind  of  juxtaposition :  but 
Everhard,  supposing  a  simultaneous  formation  of  all  the  instruments 
of  nutrition  together  and  at  first,  and  esteeming  the  mass  of  bloud 
by  reason  of  its  asperity  and  eagerness  unfit  for  nutrition,  and  rather 
apt  to  prey  upon  than  feed  the  parts,  maintains,  that  the  liquor  is 
sucked  out  of  the  amnion  by  the  mouth,  concocted  in  the  stomack, 
and  thence  passed  into  the  Milky  Vessels  even  from  the  beginning. 
Meantime  they  both  agree  in  this,  that  the  embryo  doth  breath  but 
not  feed  through  the  umbilicall  vessels.  This  our  Author  undertakes 
to  disprove;  and  having  asserted  the  mildness  of,  at  least,  many 
parts  of  the  bloud,  and  consequently  their  fitness  for  nutrition,  he 
defends  the  Harveyan  doctrine  of  the  colliquation  of  the  nourishing 
juyce  by  the  Arteries  and  its  conveyance  to  the  foetus  by  the 

In  the  third  chapter  Needham  gives  the  first  really  comparative 
account  of  the  secondary  apparatus  of  generation,  enunciating  the 
rather  obvious  rule  that  in  any  given  case  the  number  of  membranes 
exceeds  the  number  of  separate  humours  by  one.  He  affirms  that 
all  the  humours  are  nutritive  save  the  allantoic.  It  had  previously 
been  held  that  all  fish  eggs  were  of  one  humour  only,  but  he  points 
out  that  a  selachian  egg  has  its  white  and  yolk  separate.  He  gives 
the  results  of  his  chemical  experiments  at  this  point,  and  suggests 
that  the  noises  heard  from  embryos  in  utero  and  in  ovo  may  be  due 
to  the  presence  of  air  or  gas  in  the  amniotic  cavity,  thus  forming  a 
link  between  Leonardo  and  Mazin.  In  his  fourth  chapter  he  deals 
with  the  umbilical  vessels  and  the  urachus,  and  here  he  claims  priority 
over  Stensen  for  the  discovery  of  the  ductus  intestinalis  in  the  chick, 
referring  to  Robert  Boyle,  Robert  Willis,  Richard  Lower  and  Thomas 
Millington,  to  whom,  he  says,  he  showed  the  duct  before  Stensen 
published  his  observations  on  it.  The  fifth  chapter  is  concerned  with 
the  foramen  ovale,  and  the  arterial  and  venous  canals,  and  with  the 
foetal  circulation  in  general.  The  sixth  is  about  respiration  or  "bio- 
lychnium",  and  in  it  Needham  writes  against  the  conception  of  a 
vital  flame,  alleging  cold-blooded  animals,  etc.,  in  his  favour,  but 
here  he  takes  a  retrograde  step,  for  he  argues  that  the  use  of  the  lungs 
is  not  for  respiration  but  to  "comminute  the  bloud  and  so  render 
it  fit  for  a  due  circulation".  "The  seventh  and  last  chapter  contains 
a  direction  for  the  younger  Anatomists,  of  what  is  to  be  observed  in 
the  dissection  of  divers  animals  with  young,  and  first,  of  what  is 


common  to  the  viviparous,  then,  what  is  pecuHar  to  severall  of  them, 
as,  a  sow,  mare,  cow,  ewe,  she-goat,  doe,  rabbet,  bitch,  and  a  woman, 
lastly,  what  is  observable  in  an  Egg,  skate,  salmon,  frog,  etc.  All  is 
illustrated  with  divers  accurate  schemes." 

The  subsequent  course  of  chemical  embryology  in  the  seventeenth 
century  may  be  put  in  a  very  few  words.  Marguerite  du  Tertre 
incorporated  in  her  obstetrical  text-book  of  1677  the  results  of  some 
similar  experiments  to  those  of  Needham.  "If you  heat  the  (amniotic) 
liquor",  she  says,  "it  does  not  coagulate,  and  if  you  boil  it  it  flies 
away  leaving  a  crass  salt  like  urine,  but  if  you  heat  the  serosity  of 
blood,  it  solidifies  as  if  it  were  glue."  The  same  observation  was  re- 
corded by  Mauriceau  in  1687,  who  concluded,  with  some  common 
sense,  that,  as  there  was  so  little  solid  matter  present,  the  liquid  could 
not  be  very  nutritive;  and  by  Case  in  1696,  who  said,  "In  this  juice 
the  plastic  and  vivifying  force  resides,  for  although  to  our  eyes  it  looks 
in  colour  and  consistency  like  the  serum  of  the  blood,  yet  it  is  abso- 
lutely \toto  coelo]  different;  for  if  a  little  of  the  former  is  slowly  evaporated 
\si  in  cochleari  super  ignem  defines]  no  coagulation  will  ever  appear." 
Lister  said  this  once  more  in  171 1,  but  with  Boerhaave's  work  of  1732 
the  subject  entered  a  new  phase. 

In  1670  Theodore  Kerckring  published  an  adequate  work  on  foetal 
osteology,  and,  two  years  later,  de  Graaf  and  Swammerdam, 
making  full  use  of  the  opportunities  afforded  them  by  the  invention 
of  the  microscope,  described  in  detail  the  ova  of  mammalia,  thus 
demonstrating  the  truth  of  Stensen's  suggestion  of  some  years  before. 
It  is  important  to  note  that  these  workers  mistook  the  "Graafian 
follicles"  for  the  eggs — a  mistake  which  was  not  rectified  till  the  time 
of  von  Baer.  Stensen  himself  published  not  long  after  an  account 
of  these  eggs  also,  but  he  was  by  then  too  late  to  gain  the  priority 
of  demonstration.  Portal's  claim  that  Ferrari  da  Grado,  who  lived 
in  the  fifteenth  century,  was  the  true  discoverer  of  mammalian  ova 
has  been  disproved  by  Ferrari;  and,  although  it  is  true  that  Volcher 
Goiter  described  what  we  now  call  the  Graafian  follicles,  he  did  not 
recognise  in  any  way  their  true  nature. 

De  Graaf 's  discovery  was  confirmed  in  1678  by  Caspar  Bartholinus, 
and,  in  1674,  by  Langly,  whose  original  observations  had  been  made, 
so  it  was  said,  in  1657,  the  year  of  Harvey's  death.  If  this  is  true, 
Langly  has  the  priority  of  observation,  Stensen  of  theory  and  de 
Graaf  of  demonstration. 

i66  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

3-7.    Marcello  Malpighi:  Micro- Iconography  and  Preforma- 

In  the  year  1672,  Marcello  Malpighi,  who  had  for  many  years 
previously  been  working  on  various  embryological  problems  with  the 
aid  of  the  simple  microscope,  published  his  tractates  De  Ovo  Incubato 
and  De  Formatione  Pulli  in  Ovo.  In  spite  of  its  great  importance,  there 
is  not  much  to  be  said  about  it,  for  it  is  anything  but  a  voluminous 
work.  The  plates  in  which  Malpighi  represented  the  appearances  he 
had  seen  in  his  examination  of  the  embryo  at  different  stages  are 
beautiful,  and  some  of  them  are  reproduced.  Description  of  the  embryo 
was  now  pushed  back  into  the  very  first  hours  of  incubation,  and  it 
is  interesting  to  note  that  Malpighi  could  not  have  done  his  work 
without  Harvey,  whose  name  he  mentions  on  his  first  page,  and  who 
pointed  out  the  cicatricula  as  the  place  where  development  began, 
and  therefore,  as  Malpighi  must  have  reasoned,  the  place  where 
microscopic  study  would  be  very  profitable.  Now  for  the  first  time 
the  neural  groove  was  described,  the  optic  vesicles,  the  somites,  and 
the  earliest  blood-vessels. 

Malpighi  opened  the  modern  phase  of  the  controversy  preformation 
versus  epigenesis  by  supporting  the  former  view.  Embryogeny,  he 
held,  is  not  comparable  to  the  building  of  an  artificial  machine,  in 
which  one  part  is  made  after  another  part,  and  all  the  parts  gradually 
"assembled",  but  takes  place  rather  by  an  unfolding  of  what  was 
already  there,  like  a  Japanese  paper  flower  in  water.  He  was  led 
to  this  belief  by  the  fact  that  development  goes  on  after  fertilisation 
as  the  tgg  passes  down  the  oviduct,  and  in  the  most  recently  laid 
eggs  gastrulation  is  already  over,  so  that  in  his  researches  he  could 
never  find  an  absolutely  undivided  egg-cell.  It  is  curious  to  note 
that  he  says  his  experiments  were  done  "mense  Augusti,  magno  vigente 
calore'\  so  that  more  than  a  usual  degree  of  development  would 
have  taken  place  overnight.  Had  he  examined  the  cicatriculae  in 
hens'  eggs  before  laying,  he  would  very  probably  not  have  formed 
this  theory,  and  the  epigenesis  controversy  would  have  been  settled 
with  Harvey.  Another  influence  which  was  unfavourable  to  the 
epigenetic  position  was  that  it  was  Aristotelian,  and  therefore  un- 
fashionable. Yet  Malpighi's  view  was  much  more  sensible  than  many 
which  succeeded  it,  for  he  did  not  maintain  a  perfectly  equal  swelling 
up  of  all  parts  existing  at  the  start,  but  rather  an  unequal  unfolding, 

SECT.   3] 



a  distribution  of  rate  of  growth  at  different  times  and  in  different 
regions  of  the  body.  Thus  he  says,  "Now,  as  Tully  says,  Death  truly 
belongs  neither  to  the  living  nor  to  the  dead,  and  I  think  that  some- 
thing similar  holds  of  the  first  beginnings  of  animals,  for  when  we 
enquire  carefully  into  the  production  of  animals  out  of  their  eggs, 
we  always  find  the  animal  there,  so  that  our  labour  is  repaid  and  we 
see  an  emerging  manifestation  of  parts  successively,  but  never  the 
first  origin  of  any  of  them". 

Ti£  JCr 

I>e  Cue  . 


#1?     J 


Ti^  lOI. 

Fig.  8.    Malpighi's  drawings  of  the  early  stages  of  development  in  the  chick  embryo. 

What  had  been  an  unfounded  speculation  for  Seneca  in  antiquity 
and  for  Joseph  de  Aromatari  and  Everard  in  late  times  was  now  set 
upon  an  apparently  firm  experimental  basis  by  Malpighi. 

It  is  most  instructive  to  note  the  difference  in  the  attitudes  of 
Langly  and  Schrader  respectively  towards  the  preformation  question. 
Langly  has  no  doubts  about  it,  nor  has  Faber;  they  both  follow 
Harvey  and  epigenesis  unquestioningly,  but  Schrader,  although  he 
believes  in  epigenesis  on  the  whole,  is  not  at  all  certain  about  it. 
His  friend,  Matthew  Slade,  he  says,  brought  the  epistle  of  Joseph 
de  Aromatari  to  his  attention,  and  what  with  that  and  the  unexplained 
observations  of  Malpighi  on  the  pre-existence  of  the  embryo,  he  is 
not  willing  to  deny  all  value  to  preformationist  doctrine.  Others 
were  bolder.    It  was  immediately  seized  upon  by  Malebranche,  the 

1 68 


Streeter  of  his  age,  who,  in  his  Recherche  de  la  Verite  of  1672,  reaHsed 
its  philosophical  possibilities,  and  gave  it  a  kind  of  metaphysical 
sanction.  That  mystical  microscopist,  Swammerdam,  made  use  of 
it  as  an  explanation  of  the  doctrine  of  original  sin.  In  a  remarkably 
short  space  of  time  it  was  a  thoroughly  established  piece  of  biological 

Malebranche  refers  to  it  in  his  Recherche  de  la  Verite  in  the  chapter 
where  he  treats  of  optical  illusions  and  emphasises  the  deceitfulness 
and  inadequacy  of  our  senses.  "We  see",  he  says,  "in  the  germ  of  a 
fresh  Qgg  which  has  not  been  incubated  an  entirely  formed  chicken. 
We  see  frogs  in  frogs'  eggs  and  we  shall  see  other  animals  in  their 


Fig.  9.   Malpighi's  drawings  of  the  chick  embryo's  blood-vessels. 

germs  also  when  we  have  sufficient  skill  and  experience  to  discover 
them.  We  must  suppose  that  all  the  bodies  of  men  and  animals  which 
will  be  born  until  the  consummation  of  time  will  have  been  direct 
products  of  the  original  creation,  in  other  words,  that  the  first  females 
were  created  with  all  the  subsequent  individuals  of  their  own  species 
within  them.  We  might  push  this  thought  further  and  belike  with 
much  reason  and  truth,  but  we  not  unreasonably  fear  a  too  premature 
penetration  into  the  works  of  God.  Our  thoughts  are,  indeed,  too 
gross  and  feeble  to  understand  even  the  smallest  of  his  creatures." 
Malebranche,  who  was  a  priest  of  the  Oratory  of  the  Cardinal  de 
Berulle,  took  an  ardent  interest  in  the  scientific  life  of  his  time — for 
example,  in  a  letter  to  Poisson,  the  Abbe  Daniel  wrote,  "Reverend 
Father,  M.  Malebranche  has  written  to  me  saying  that  he  has  in- 
stalled an  oven  in  which  he  has  hatched  eggs.  He  has  already  opened 



lu   Ouc 


Showing  the  early  stages  of  the  development  of  the  chick,  somites,  area  vasculosa,  etc. 


some  and  has  been  able  to  see  the  heart  formed  in  them  and  beating, 
together  with  some  of  the  arteries"  (Blampignon). 

Swammerdam's  support  for  preformation  came  from  a  different 
angle.  He  had  been  investigating  insect  metamorphosis,  and,  having 
hardened  the  chrysalis  with  alcohol,  had  seen  the  butterfly  folded 
up  and  perfectly  formed  within  the  cocoon.  He  concluded  that  the 
butterfly  had  been  hidden  or  masked  {larvatus)  in  the  caterpillar,  and 
thence  it  was  no  great  step  to  regard  the  Qgg  in  a  similar  light.  Each 
butterfly  in  each  cocoon  must  contain  eggs  within  it  which  in  their 
turn  must  contain  butterflies  which  in  their  turn  must  contain  eggs, 
and  so  on.  Before  long,  Swammerdam  extended  this  theory  to  man. 
"In  nature",  he  said,  "there  is  no  generation  but  only  propagation, 
the  growth  of  parts.  Thus  original  sin  is  explained,  for  all  men  were 
contained  in  the  organs  of  Adam  and  of  Eve.  When  their  stock  of 
eggs  is  finished,  the  human  race  will  cease  to  be." 

In  1684  Zypaeus  reported  that  he  had  seen  minute  embryos  in 
unfertilised  eggs,  and  there  were  other  similar  claims.  ''^Hinc  recentiores 
physiologV\  said  Schurigius  in  1732,  ^^  hominem  in  ovulis  delineatum 
quoad  omnes  partes  in  exiguis  staminibus  ante  conceptionem  existere 

Swammerdam  cannot  be  regarded  simply  as  one  of  the  principal 
pillars  of  the  preformation  theory.  His  own  embryological  researches, 
which  were  made  chiefly  on  the  frog,  were  remarkable  in  many 
ways.  He  was  the  first  to  see  and  describe  the  cleavage  of  the  egg- 
cell  and  later  segmentation.  He  said  that  there  was  a  time  during  the 
development  of  the  tadpole  when  its  body  consisted  of  granules 
{greynkens  or  klootkens),  but  as  these  grew  smaller  and  much  more 
numerous  they  escaped  his  penetration.  Leeuwenhoek  also  saw  these 
cells,  and  his  account  was  published  long  before  Swammerdam's, 
but  his  observations  on  the  rotating  embryos  oi  Anodon  and  the  eggs 
of  fleas  were  equally  interesting. 

3-8.    Robert  Boyle  and  John  Mayow 

In  1674  John  Mayow,  a  young  Oxford  physician,  published  his 
tractate,  De  Respiratione  Foetus  in  Utero  et  Ovo,  which  was  included  as 
one  of  the  parts  of  his  Tractatus  Quinque  medico-physici  in  that  year. 
Mayow  was  the  first  worker  to  realise  that  gaseous  oxygen,  or,  as  he 
termed  it,  the  "  nitro-aerial "  vapour,  was  the  essential  factor  in  the 
burning  of  a  candle  and  the  respiration  of  a  living  animal.  His  work 

170  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

was  forgotten  until  Beddoes  drew  attention  to  it  in  1 790,  but  since  then 
many  have  praised  it  and  Schultze  makes  him  the  equal  of  Harvey. 

The  reason  why  he  became  interested  in  embryology  is  given  in 
the  opening  sentences  of  his  work.  "Since  the  necessity  of  breathing", 
he  says,  "is  so  essential  to  the  sustaining  of  life  that  to  be  deprived 
of  air  is  the  same  as  to  be  deprived  of  common  light  and  vital  spirit, 
it  will  not  be  out  of  place  to  enquire  here  how  it  happens  that  the 
foetus  can  live  though  imprisoned  in  the  straits  of  the  womb  and 
completely  destitute  of  air."  He  first  of  all  gives  an  account  of  the 
opinions  held  about  foetal  respiration  and  the  umbilical  cord.  He 
says  that  he  disagrees  (i)  with  the  view  that  the  embryo  breathes 
per  OS  while  it  is  in  the  womb,  for  there  is  no  air  in  the  amnion  and 
the  suctio  infantuli  proves  nothing;  and  (2)  with  the  view  pro- 
pounded by  Spigelius  that  the  umbilical  vessels  existed  to  supply 
blood  to  the  placenta  for  the  nourishment  of  the  latter.  If  this  were 
the  case,  he  says,  the  membranes  in  the  hen's  egg  could  not  be  formed 
before  the  vitelline  vein,  as  they  are,  and  in  cases  of  foetal  atrophy 
the  placenta  would  always  die  and  be  corrupted  too,  which  does  not 
happen.  Nor  does  he  support  the  view  of  Harvey  (3)  that  the 
umbilical  vessels  supply  blood  for  the  concoction  and  colliquation 
of  the  food  of  the  foetus,  for  why  should  not  the  embryonic  body 
prepare  its  own  nutritious  juice  before  birth  just  as  it  does  afterwards. 
He  further  thinks  the  theory  (4)  that  the  umbilical  vessels  are  for 
carrying  off  surplus  foetal  nourishment  quite  untenable  and  as  little 
likely  as  the  theory  (5)  that  they  exist  for  the  object  of  allowing  a 
foetal  circulation — for  this  could  just  as  well  be  accomplished  through 
the  vessels  which  exist  in  the  embryonic  body. 

Mayow  decides  therefore  for  the  opinion  of  divino  sene  Hippo- 
crate  and  Everard  that  the  umbilicus  is  a  respiratory  mechanism, 
carefully  dissociating  himself,  however,  from  the  hypothesis  of 
Riolanus  that  the  umbilical  cord  with  all  its  windings  is  so  arranged 
to  cool  the  blood  passing  through  it.  He  then  says,  "We  observe, 
in  the  first  place,  that  it  is  probable  that  the  albuminous  juice  exuding 
from  the  impregnated  uterus  is  stored  with  no  small  abundance  of 
aerial  substance,  as  may  be  observed  from  its  white  colour  and  frothy 
character  [Needham's  uterine  milk].  And  in  further  indication  of 
this,  the  primogenial  juices  of  the  egg,  which  have  a  great  resemblance 
to  the  seminal  juice  of  the  uterus,  appear  to  abound  in  air  particles. 
For  if  the  white  or  the  yolk  of  an  tgg  be  put  into  a  glass  from  which 


the  air  is  exhausted  by  the  Boyhan  pump  these  liquids  will  imme- 
diately become  very  frothy  and  swell  up  into  an  almost  infinite 
number  of  little  bubbles  and  into  a  much  greater  bulk  than  before — a 
sufficiently  clear  proof  that  certain  aerial  particles  are  most  intimately 
mixed  with  these  liquids.  To  which  I  add  that  the  humours  of  an 
tgg  when  thrown  into  the  fire,  give  out  a  succession  of  explosive 
cracks  which  seem  to  be  caused  by  the  air  particles  rarefying  and 
violently  bursting  through  the  barriers  which  confined  them.  Hence 
it  is  that  the  fluids  of  the  egg  are  possessed  of  so  fermentative  a  nature. 
For  it  is  indeed  probable  that  the  spermatic  portions  of  the  uterus 
and  its  carunculae  are  naturally  adapted  for  separating  aerial  particles 
from  arterial  blood.  These  observations  premised,  we  maintain  that 
the  blood  of  the  embryo,  conveyed  by  the  umbilical  arteries  to  the 
placenta  or  uterine  carunculae,  brings  not  only  nutritious  juice,  but 
along  with  this  a  portion  of  nitro-aerial  particles  to  the  foetus  for 
its  support,  so  that  it  seems  that  the  blood  of  the  infant  is  impregnated 
with  nitro-aerial  particles  by  its  circulation  through  the  umbilical 
vessels  quite  in  the  same  way  as  in  the  pulmonary  vessels.  And  there- 
fore I  think  that  the  placenta  should  no  longer  be  called  a  uterine 
liver  but  rather  a  uterine  lung".  These  splendid  words,  informed  by 
so  much  insight  and  scientific  acumen,  show  that,  by  the  time  of 
Mayow,  chemical  embryology  had  definitely  come  into  being.  He  died 
at  the  early  age  of  thirty-six,  and  we  may  well  ponder  how  different 
the  subsequent  course  of  this  kind  of  study  would  have  been  if  he  had 
lived  a  little  longer. 

The  second  part  of  Mayow's  treatise  is  concerned  with  respiration 
in  the  hen's  egg  during  its  development,  and  it  may  be  noted  that 
his  observations  on  the  air  contained  in  the  liquids  before  develop- 
ment probably  account  for  the  facts  which  have  been  reported  at 
one  time  and  another  concerning  an  alleged  anaerobic  life  of  embryos 
in  early  stages.  Mayow  is  wrong  in  supposing  that  the  gas  which  he 
pumped  out  from  white  and  yolk  was  purely  "nitro-aerial",  but  he 
shows  the  greatest  good  sense  in  his  reminder  that  the  amount  of 
nitro-aerial  particles  required  by  embryos  must  be  comparatively 
small  owing  to  their  small  requirement  for  "muscular  contraction 
and  visceral  concoction".  His  remarks  on  the  effect  of  heat  on  the 
developing  egg  are  not  so  clear  as  the  remainder  of  the  treatise,  but 
he  seems  to  mean  that  the  heat  will  disengage  the  nitro-aerial  particles 
from  the  liquids,  and  so  aid  in  respiration,  an  idea  which  was  later 

172  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

used  by  Mazin.  His  fundamental  mistake  here  was  that  he  failed  to 
realise  that  the  egg-shell  was  permeable  to  air;  and  this  vitiates  all 
his  reasoning  about  the  respiration  of  the  egg.  "It  will  not  be  ir- 
relevant", he  says,  "to  enquire  here  whether  the  air  which  is  con- 
tained in  the  cavity  in  the  blunter  end  of  every  egg  contributes  to 
the  respiration  of  the  chick."  He  first  notes  that  the  cavity  in  question 
lies  between  two  membranes  and  not  between  the  shell-membrane 
and  the  shell  as  Harvey  himself  had  supposed ;  and  then  he  goes  on 
to  say  that  he  disagrees  with  the  opinion  of  Fabricius,  who  had  asserted 
that  the  air  in  the  air-space  serves  for  the  respiration  of  the  chick. 
His  reasons  are  (i)  that  there  would  not  be  enough  therein  for  the 
needs  of  the  embryo  which  would  use  it,  as  it  were,  in  one  gulp, 
and  (2)  that  the  air  in  it  cannot  pass  through  the  inner  membrane, 
an  error  into  which  he  was  led  by  observing  that,  if  an  egg-shell 
with  its  contents  removed  and  its  air-space  intact,  was  put  into  a 
vacuum,  the  air-space  would  swell  up  until  it  was  as  big  as  the  egg 
itself.  Mayow  sees  now  what  had  escaped  the  attention  of  all  previous 
observers,  namely,  that  the  egg-contents  are  not  "rarefied  or  ex- 
panded, but  are  on  the  contrary  condensed  and  forced  into  a  nar- 
rower space  than  before".  Such  a  condensation  could,  he  thinks, 
take  place  in  four  ways,  (a)  by  an  increase  in  propinquity  of  discrete 
particles,  (b)  by  a  subsidence  of  motion  on  the  part  of  a  congregation 
of  particles  into  rest,  (c)  by  the  extraction  of  some  subtle  spirit  from 
amongst  the  particles,  and,  (d)  by  a  decrease  in  elasticity  on  the  part 
of  some  elastic  substance  previously  present.  We  should  at  the  present 
time  choose  the  third  alternative  as  being  the  truest,  in  view  of  the 
loss  of  water  and  carbon  dioxide  which  the  egg  suffers  as  it  develops, 
but  Mayow  chose  the  fourth,  thinking  it  probable  that  the  "air 
distributed  among  the  juices  of  the  egg  loses  its  elastic  force  on  account 
of  the  fermentation  produced  among  these  juices  by  incubation". 
Now  since  the  egg-contents  are  compacted  into  smaller  bulk  by  the 
process  of  incubation,  a  vacuum  would  be  created  somewhere  if 
Nature  had  not,  with  her  customary  prudence,  inserted  a  small 
amount  of  air  into  the  air-space  which  might  in  due  course  expand 
and  avoid  this.  His  proof  for  this  was  an  inaccurate  observation; 
he  thought  he  saw,  in  eggs  at  a  late  stage,  when  the  contents  were 
removed,  the  air-space  collapse  to  the  normal  size  which  it  occupies 
in  unincubated  eggs.  He  expressly  says  that  his  theory  does  not  depend 
upon  the  conception  of  horror  vacui,  but  that,  by  the  compressive 


action  of  the  imprisoned  air,  the  fluids  of  the  egg  would  be  forced  into 
the  umbiHcal  vessels,  and  the  particles  composing  the  embryonic  body 
packed  more  tightly  together.  "The  internal  air  appears  to  perform 
the  same  work  as  the  steel  plate  bent  round  into  numerous  coils  by 
which  automata  are  set  in  motion." 

With  this  ingenious  but  erroneous  supposition  Mayow  concludes 
what  is  undoubtedly  the  first  great  contribution  to  physiological  or 
biophysical  embryology.  His  views  on  foetal  respiration  were  soon 
generally  accepted,  as  the  writings  of  Zacchias,  Viardel,  Pechlin  and 
John  Ray  show,  but  Sponius  as  late  as  1684  was  asserting  that  the 
lungs  of  the  foetus  were  functional  in  utero,  absorbing  from  the 
amniotic  liquid  the  nitro-aerial  particles  which  P.  Stalpartius  sup- 
posed the  placenta  to  be  secreting  into  it.  It  is  interesting  to  note 
that  by  Mayow's  own  air-pump  method  Bohn  found  nitro-aerial 
particles  in  the  uterine  milk  in  1686,  and  Lang  found  them  in  the 
amniotic  liquid  in  1 704.  The  problem  had  by  then  arrived  at  a  stage 
beyond  which  it  could  not  progress  in  the  absence  of  quantitative 

The  year  1675  saw  the  publication  of  Nicholas  Hoboken's  useful 
treatise  on  the  anatomy  of  the  placenta,  and  of  the  English  edition 
of  P.  Thibaut's  Art  of  Chymistry.  I  mention  the  latter  here,  because 
of  a  reference  to  the  special  conditions  of  embryonic  life  which  is 
found  in  it.  As  yet  no  real  help  was  being  given  to  embryology  by 
contemporary  chemistry. 

The  Magistery  and  Calx  of  Egg-shells. 

Obs.  2.  That  you  must  use  the  eggshells  of  hens  and  not  of  ducks,  geese, 
or  turkeys  because  that  hens  eggshells  easier  calcin'd  being  thinner  by 
reason  that  a  hen  is  a  more  temperate  animall;  waterfowl  are  hotter  and 
by  reason  of  their  heat  do  concoct  and  harden  their  eggshells  more  than 
other  fowl ;  and  from  thence  it  comes  that  you  must  have  a  greater  quantity 
of  your  Dissolvant,  employ  more  heat,  and  spend  more  time  to  calcine 
the  eggs  of  waterfowl  than  those  of  hens. 

About  this  time  also  Francis  Willoughby  published  his  famous 
book  on  birds,  an  attempt  to  bring  Aldrovandus  up  to  date,  in  which 
a  good  picture  is  given  of  the  embryological  knowledge  of  the  time, 
although  no  new  observations  or  theories  are  given.  Another  con- 
temporary review  is  that  of  Barbatus. 

In  1677,  spermatozoa  were  discovered,  as  announced  by  Hamm 
and  Leeuwenhoek  in  the  Philosophical  Transactions  of  the  Royal  Society, 

174  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

though  Hartsoeker  afterwards  claimed  that  he  had  seen  them  as 
early  as  1674,  but  had  not  had  sufficient  confidence  to  publish  his 
results.  There  is  a  reference  to  this  in  the  letters  of  Sir  Thomas 
Browne,  who,  writing  to  his  son,  Dr  Edward  Browne,  on  December  9, 
1679,  said,  "I  sawe  the  last  transactions,  or  philosophicall  col- 
lections, of  the  Royal  Society.  Here  are  some  things  remarkable,  as 
Lewenhoecks  finding  such  a  vast  number  of  little  animals  in  the  melt 
of  a  cod,  or  the  liquor  which  runnes  from  it ;  as  also  in  a  pike ;  and 
computeth  that  they  much  exceed  the  number  of  men  upon  the  whole 
earth  at  one  time,  though  hee  computes  that  there  may  bee  thirteen 
thousand  millions  of  men  upon  the  whole  earth,  which  is  very  many. 
It  may  bee  worth  your  reading". 

At  the  same  time  as  these  events  were  taking  place,  Robert  Boyle, 
at  Oxford  and  London,  was  engaged  in  carrying  out  those  experi- 
ments in  chemistry  which  led  him  before  long  to  write  his  Sceptical 
Chymist.  It  is  not  generally  known  that  in  this  work,  which  appeared 
in  1680,  and  which  set  the  key  for  the  whole  spirit  of  subsequent 
physico-chemical  research,  Boyle  has  a  reference  to  embryology,  and, 
curiously  enough,  in  connection  with  a  point  which,  although  it  is 
easily  seen  to  be  of  the  highest  importance,  has  been  quite  overlooked 
by  the  commentators  upon  him.  One  of  the  main  things  he  was 
trying  to  urge  was  that,  until  some  system  could  be  proposed  which 
would  give  a  means  of  quantitative  estimation  of  the  constituents  of 
a  mixture,  no  further  progress  would  be  made.  He  was  asking,  in 
fact,  that  chemistry  should  become  an  exact  science,  and  his  demand 
is  only  veiled  by  the  unfamiliarity  of  his  language.  His  preference 
for  the  "mechanical  or  corpuscularian"  philosophy  was  mainly  due 
to  his  realisation  that,  unless  chemistry  was  going  to  start  measuring 
something,  it  might  as  well  languish  in  the  obscurity  to  which 
Harvey  would  have  willingly  relegated  it.  Thus  he  says,  "But  I 
should  perchance  forgive  the  Hypothesis  I  have  been  all  this  time 
examining  (that  of  the  alchemists),  if,  though  it  reaches  but  to  a 
very  little  part  of  the  world,  it  did  at  least  give  us  a  satisfactory  account 
of  those  things  which  'tis  said  to  teach.  But  I  find  not  that  it  gives 
us  any  other  than  a  very  imperfect  information  even  about  mixt 
bodies  themselves;  for  how  will  the  knowledge  of  the  Tria  Prima 
discover  to  us  the  reason  why  the  Loadstone  drawes  a  Needle,  and 
disposes  it  to  respect  the  Poles,  and  yet  seldom  precisely  points  at 
them?  how  will  this  hypothesis  teach  us  how  a  Chick  is  formed 

SECT.  3] 



in  the  Egge,  or  how  the  seminal  principles  of  mint,  pompions,  and 
other  vegetables,  can  fashion  Water  into  various  plants,  each  of  them 
endow'd  with  its  peculiar  and  determinate  shape  and  with  divers 
specifick  and  discriminating  Qualities?  How  does  this  hypothesis 
shew  us,  how  much  Salt,  how  much  Sulphur,  how  much  Mercury  must  be 
taken  to  make  a  Chick  or  a  Pompion?  and  if  we  know  that,  what 
principle  is  it,  that  manages  these  ingredients  and  contrives,  for 
instance,  such  liquors  as  the  White  and  Yolke  of  an  Egge  into  such 
a  variety  of  textures  as  is  requisite  to  fashion  the  Bones,  Arteries, 
Veines,  Nerves,  Tendons,  Feathers,  Blood  and  other  parts  of  a  Chick; 
and  not  only  to  fashion  each  Limbe,  but  to  connect  them  altogether, 
after  that  manner  which  is  most  congruous  to  the  perfection  of  the 
Animal  which  is  to  consist  of  them?  For  to  say  that  some  more  fine 
and  subtile  part  of  either  or  all  the  Hypostatical  Principles  is  the 
Director  in  all  the  business  and  the  Architect  of  all  this  elaborate 
structure,  is  to  give  one  occasion  to  demand  again,  what  proportion 
and  way  of  mixture  of  the  Tria  Prima  afforded  this  Architectonick 
Spirit,  and  what  Agent  made  so  skilful  and  happy  a  mixture?" 
Boyle's  instance  of  the  magnetic  needle  pointing  nearly,  not  exactly, 
at  the  north,  and  his  use  of  the  expressions  "how  much,  how  many, 
proportion,  way  of  mixture",  indicate  that  he  was  moving  towards 
a  quantitative  chemistry,  and  by  express  implication  a  quantitative 
embryology.  Elsewhere  he  says  that  he  thinks  the  Tria  Prima  will 
hardly  explain  a  tenth  part  of  the  phenomena  which  the  "Leucip- 
pian"  or  atomistic  hypothesis  is  competent  to  deal  with.  Thus, 
although  Boyle  made  few  experiments  or  observations  on  embryos, 
he  occupies  a  very  important  position  in  the  history  of  embryology. 
During  the  last  two  decades  of  this  century,  the  Oxford  Philo- 
sophical Society  were  occupied  on  a  good  many  occasions  with 
problems  relating  to  embryology.  It  is  extremely  interesting  to  note, 
in  connection  with  what  we  have  just  seen  in  Boyle,  that  John 
Standard  of  Merton  College  reported  on  February  10,  1685,  "the 
following  obbs.  concerning  ye  weight  of  ye  severall  parts  of  Henn's 
eggs ;  done  with  a  pair  of  scales  which  turned  with  \  a  grain. 

ozs.  dr. 

A  henn's  egg  weighed  2 

The  skin  weighed 

The  shell 
The  yolk 
The  white 





Loss  in  weighing 

[ujf  LIBRARY 

176  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  11 

ozs.  dr.  scr.  grns. 

Another  raw  egg  of  the  same  sort     ...         2  i  2  13 


The  former  egg  boiled 

Lost  in  boiling 

The  skin 

The  shell 

The  yolk 

The  white 

2                  I  I  19 

.2                  I  I  18 

•         -                 -  -  15 


-  I  2  19 

-  5  -  7 
I                  2  -  13 

Loss  in  weighing       5 

Another  early  quantitative  observation  was  that  of  Claude  Perrault 
who  found  about  1680  that  developing  ostrich  eggs  lost  one-ninth 
of  their  weight  in  five  weeks.  The  Oxford  Philosophical  Society, 
however,  preferred  as  a  rule  to  consider  more  unusual  things,  such 
as  "the  egges  of  a  parrot  hatched  in  a  woeman's  bosome,  a  hen  egg 
figur'd  like  a  bottle,  a  hen  egg  that  at  the  big  ende  had  a  fleshie 
excrescence,  another  hen-eg,  monstrous,  a  suppos'd  cocks  egg,  and 
the  eggs  of  a  puffin,  an  elligug,  and  a  razor-bill".  Mention  of  these 
different  kinds  of  eggs  reminds  us  that  the  systematic  collection  and 
classification  of  eggs  had  been  begun  some  years  before  by  Sir  Thomas 
Browne  (as  may  be  seen  in  John  Evelyn)  and  by  John  Tradescant. 
About  this  time  R.  Waller  made  some  noteworthy  observations  on 
the  "spawn  of  frogs  and  the  production  of  Todpoles  therefrom", 
extending  the  work  begun  by  Swammerdam  not  long  before. 
Mauriceau  now  gave  a  description  of  the  phenomenon  of  sterile 
foetal  atrophy.  The  century  fittingly  closes  with  Michael  Ettmiiller's 
ponderous  treatise,  in  which  all  the  embryological  work  of  the 
seventeenth  century  is  summarised  with  considerable  accuracy.  He 
supported  the  moribund  menstruation  theory  of  embryogeny  with 
the  argument  that  animals  do  not  menstruate  because  they  are  more 
prolific  than  men,  and  therefore  all  their  blood  is  required  for  genera- 
tion. Garmann's  Oologia  curiosa,  which  appeared  in  1691,  is  worth 
mention  also,  as  a  review  of  the  knowledge  of  the  time.  But  that  his 
work  was  what  the  booksellers'  catalogues  describe  as  "curious"  is 
shown  by  the  following  chapter-headings:  De  ovo  mystico,  rnpthico, 
magico,  mechanico,  medico,  spagyrico,  magyrico,  pharmaceutico. 

3-9.    The  Theories  of  Foetal  Nutrition 

During  the  course  of  the  seventeenth,  and  the  first  quarter  of  the 
eighteenth,  century,  many  theories  were  propounded  concerning 
foetal  nutrition.    It  is  convenient  to  classify  them. 


I.   That  the  embryo  was  nourished  by  the  menstrual  blood. 

Beckher,  1633. 

Plempius,  1644.    (He  did  not  deny  that  the  umbilical  cord  was 

functional,  but  insisted  that  the  blood  passing  through  it  was 


In  1 65 1  Harvey's  work  was  published. 
Sennertus,  1654. 
Seger,  1660. 
van  Linde,  1672. 
F.  Sylvius,  1680. 
Cyprianus,  1700. 

II.    That  the  embryo  was  nourished  by  its  mouth. 
{a)  By  the  amniotic  liquid. 

(A)    In  addition  to  the  umbilical  blood. 
Harvey,  1651. 
W.  Needham,  1667. 
de  Graaf,  1677. 

C.  Bartholinus,  1679. 
van  Diemerbroeck,  1685. 
Ortlob,  1697. 

D.  Tauvry,  1700. 
Linsing,  1701. 
PauH,  1707. 
Barthold,  1717. 

S.  Middlebeek,  17 19. 
Teichmeyer,  17 19. 
Gibson,  1726. 

(B)  Alone;   the  umbilical  blood  being  regarded  as  un- 
necessary or  of  minor  importance, 
Moellenbroeck,  1672. 
Cosmopolita,  1686. 
Everardus,  1686. 
P.  Stalpartius,  1687. 
Bierling,  1690. 

Case,  1696.   (Case  thought  the  embryo  arose  entirely 
out  of  the  amniotic  liquid  like  a  precipitate  from 
a  clear  solution.) 
Berger,  1702. 

These  persons  referred  as  their  principal  experi- 
mental basis  to  cases  in  which  embryos  had  been 
born  without  umbilical  cords,  e.g.  of  those  of: 
Rommelius,  1675  (in  Velsch). 
Valentinius,  1 7 1 1 . 

178  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

(b)  By  the  uterine  milk  or  succum  lacteo-chylosum. 

Mercklin,  1679. 
Drelincurtius,  1685. 
Bohnius,  1686. 
Zacchias,  1688. 
Tauvry,  1694. 
Franc,  1722. 
Dionis,  1724. 

III.    That  the  embryo  was  nourished  through  the  umbiHcal  cord 

{a)  By  foetal  blood  (the  circulations  distinct). 

Arantius,  1595. 

Harvey,  1651. 

W.  Needham,  1667. 

F.  Hoffmann,  1681.  (He  proved  the  point  by  injection 
long  before  Hunter,  who  is  stated  by  Cole  to  have  been 
the  first  to  demonstrate  this.) 

Ruysch,  1 70 1. 

Snelle,  1705. 

Falconnet,  171 1. 

It  is  to  be  noted  that  Bierling,  P.  Stalpartius,  Berger, 
Barthold,  and  Charleton,  who  supported  the  discon- 
tinuity theory  of  the  circulations,  were  all  upholders 
of  the  theory  of  foetal  nourishment  per  os,  so  that  their 
reasons  for  doing  so  were  not  those  on  account  of 
which  we  agree  with  Hoffmann  and  Needham  at  the 
present  time. 

{b)  By  maternal  blood  (the  circulations  continuous). 

Laurentius,  1600. 

de  Marchette,  1656. 

Rallius,  1669. 

Muraltus,  1672. 

Blasius,  1677. 

Veslingius,  1677. 

Hamel,  1700. 

de  Craan,  1703. 

Lang,  1704. 

van  Home,  1707. 

Freind,  171 1.  (Freind's  Emmenologia  deserves  a  special 
mention.  He  proved  by  a  calculation  that  the  amount 
of  blood  passing  through  the  umbilical  cord  would  be 
sufficient  for  the  needs  of  the  embryo.  This  is  a  parallel 
to  Harvey's  famous  calculation  about  the  circulation 
of  the  blood.    He  also  quotes  some  experiments  of 


Rayger  and  Gayant,  who  injected  a  blue  dye  into  the 
foetal  circulation  and  found  it  again  in  the  maternal. 
Therefore  he  regards  it  as  continuous.) 

Mery,  171 1.  (Mery  combated  Falconnet's  view  of  the 
separate  circulations.  He  said  that  he  had  not  himself 
tried  Falconnet's  experiment,  but  that  some  students 
had,  and  could  not  repeat  it.) 

Aubert,  1 7 1 1 .  (Narrative  of  a  case  in  which  the  um- 
bilical cord  had  not  been  tied  at  the  maternal  end  and 
the  mother  had  nearly  bled  to  death  through  it.) 

Nenterus,  17 14. 

Wedel,  1 71 7. 

Bellinger,  171 7.  (Bellinger  believed  that  the  maternal 
blood  was  transformed  by  the  embryonic  thymus  gland 
into  proper  nourishment  for  itself,  after  which  it  was 
secreted  into  the  mouth  by  the  salivary  ducts  and  so 
went  to  form  meconium  without  the  necessity  for  de- 
glutination.  Heister's  comments  on  this  extraordinary 
theory  are  worth  reading.  Perhaps  Bellinger  was  in- 
debted to  Tauvry  for  his  idea  of  the  importance  of  the 
thymus  gland.  Tauvry  had  drawn  attention  in  1700 
to  its  diminution  after  birth.) 

de  Smidt,  17 18. 

Dionis,  1724. 

(c)  By  menstrual  blood. 

Plempius,  1644. 

(d)  By  uterine  milk. 

Ent,  1687. 

Camerarius,  17 14.    {Opinio  conciliatrix!) 

F.  Hoffmann,  1718. 

{e)  By  the  amniotic  fluid. 

Vicarius,  1700. 
Goelicke,  1723. 

IV.   That  the  embryo  was  nourished  by  pores  in  its  skin. 

Deusingius,  1660. 
Nitzsch,  1 67 1. 
Stockhamer,  1682. 

This  was  suggested  on  the  ground  that  in  the  earlier  stages  of 
development  there  is  no  umbilical  cord.  In  1684  St  Romain  argued 
against  it  on  the  ground  that,  if  it  were  true,  the  embryo  would 
dissolve  in  the  amniotic  liquid. 

i8o  EMBRYOLOGY   IN  THE   SEVENTEENTH       [pt.  ii 

During  this  period  also  there  were  continued  disputes  about  the 
origin  of  the  amniotic  liquid,  van  Diemerbroeck  and  Verheyen  con- 
sidered that  it  could  not  be  the  sweat  of  the  embryo,  for  the  embryo 
was  always  much  too  small  to  account  for  it,  and,  moreover,  Tertre 
had  described  cases  where  the  secundines  had  been  formed  with  the 
membranes  but  in  the  absence  of  the  embryo.  Dionis  affirmed  that, 
whatever  it  was,  it  could  not  be  urine,  for  urine  will  not  keep  good 
for  nine  days,  a  fortiori  not  for  nine  months.  Drelincurtius  put 
forward  a  theory  that  the  embryo  secreted  it  from  its  eyes  and  mouth 
by  crying  and  salivating,  while  Bohn  and  Blancard  derived  it  from 
the  foetal  breasts.  Lang,  Berger  and  Gofey  criticised  this  notion 
without  bringing  forward  anything  constructive,  and  Gofey  was  in 
his  turn  annihilated  by  D.  Hoffmann,  who  with  Nenter  and  Konig 
supported  the  modern  view,  namely,  that  it  was  a  transudation  from 
the  maternal  blood-vessels  in  the  decidua.  The  question  was  com- 
plicated further  by  the  alleged  discovery  by  Bidloo  in  1 685  of  glands 
in  the  umbilical  cord,  and  by  Vieussens  in  1 705  of  glands  on  the 
amniotic  membrane.  J.  M.  Hoffmann  and  Nicholas  Hoboken  sup- 
ported the  view  that  these  were  the  important  structures.  There  the 
problem  was  left  during  the  eighteenth  century,  various  writers 
supporting  different  opinions  from  time  to  time,  and  it  is  still  under 
discussion  (see  Section  22). 

Very  early  in  the  eighteenth  century  (1708)  there  appeared  a 
work  by  G.  E.  Stahl,  van  Helmont's  most  famous  follower,  which 
struck  the  keynote  of  the  whole  century.  Stahl's  Theoria  Medica  Vera, 
divided  as  it  was  into  Physiological  and  Pathological  sections,  be- 
longed in  essence  to  the  a  priori  school  of  Descartes  and  Gassendi. 
It  differed  from  them  profoundly,  of  course,  for,  instead  of  trying  to 
explain  all  biological  phenomena,  including  embryonic  develop- 
ment, from  mechanical  first  principles,  it  started  out  from  first 
principles  of  a  vitalistic  order,  and,  having  combined  all  the  archaei 
into  one  informing  soul,  it  sought  to  show  how  the  facts  could 
be  perfectly  well  explained  on  this  basis.  But  the  spiritual  kinship 
of  Stahl  with  Descartes  and  Gassendi  is  due  to  an  atmosphere 
which  can  only  be  called  doctrinaire,  and  which  was  common 
to  them  all.  Like  the  methodist  school  of  Hellenistic  medicine, 
they  subordinated  the  data  to  a  preconceived  theory,  during  which 
process  any  awkward  facts  were  liable  to  be  rather  submerged  than 


In  1722  Antoine  Maitre-Jan  published  his  book  on  the  embryology 
of  the  chick,  the  only  one  on  this  subject  between  Malpighi  and 
Haller.  It  was  an  admirable  treatise,  illustrated  with  many  drawings 
which,  though  not  very  beautiful,  were  as  accurate  as  could  be 
expected  at  the  time.  Perhaps  its  most  remarkable  characteristic 
is  its  almost  complete  freedom  from  all  theory — Maitre-Jan  says 
hardly  a  word  about  generation  in  general,  and  is  far  from  putting 
forward  a  "system"  in  the  usual  eighteenth-century  manner.  He 
contents  himself  with  the  recital  of  the  known  facts,  including  those 
added  by  his  own  observations.  He  gives  no  references,  and  writes 
in  an  extremely  modern  and  unaffected  style. 

The  only  traces  of  theoretical  presupposition  which  can  be  found 
in  him  are  Cartesian,  for  he  speaks  of  the  activity  of  ferments  in 
blood-formation.  He  is  an  epigenesist,  and  long  before  Brooks,  he  gives 
the  right  explanation  of  Malpighi's  error,  affirming  that  the  hot 
Italian  summer  was  responsible  for  some  development  in  Malpighi's 
eggs  before  Malpighi  examined  them.  Maitre-Jan's  book  must  have 
been  accessible  both  to  Buffon  and  Haller,  so  it  is  difficult  to  see  why 
they  should  have  perpetuated  Malpighi's  mistake  till  nearly  the  end 
of  the  century. 

In  technique,  Maitre-Jan  was  pre-eminent.  He  was  the  first 
embryologist  to  make  practical  use  of  Boyle's  suggestion  regarding 
"distilled  spirits  of  vinegar"  for  hardening  the  embryo  so  that  it 
could  be  better  dissected.  He  also  used  "weak  spirits  of  vitriol"; 
after  treating  blastoderms  with  it,  he  said,  "I  saw  with  pleasure  an 
infinity  of  little  capillary  vessels  which  had  not  appeared  to  be  there 
before".  He  made  a  few  chemical  experiments  also,  noting  that 
vinegar  would  coagulate  egg-white,  and  estimating  quantitatively 
the  difference  in  oil-content  of  different  yolks — though  for  this  he 
gives  no  figures. 

His  theory  he  relegated  to  an  appendix  entitled  Objections  sur 
la  generation  des  animaux  par  de  petits  vers.  There  were  sixteen  of 
them,  but  the  most  cogent  one  was  that,  as  little  worms  had  been 
found  under  the  microscope  in  pond-water,  vinegar,  and  all  kinds 
of  liquids,  there  was  no  reason  to  suppose  that  those  in  the  semen 
were  in  any  essential  way  connected  with  generation.  For  his  time, 
this  argument  was  an  excellent  one,  and  was  open  to  no  demur 
save  on  the  ground  of  filtration  experiments  which  had  not  yet  been 
made  (see  p.  215). 

i82  EMBRYOLOGY   IN   THE   SEVENTEENTH        [pt.  ii 

About  this  time  there  was  some  controversy  over  the  circulation 
of  blood,  the  foramen  ovale,  etc.,  in  the  embryo.  From  1700  to  1710, 
Tauvry  and  Mery  were  engaged  in  a  polemic  on  this  subject,  and 
the  latter  also  corresponded  with  Duverney,  Silvestre  and  Buissiere 
in  a  controversy  which  recalls  that  of  Laurentius  and  Petreus  a 
hundred  years  before.  Nicholls  wrote  later  on  the  same  subject. 
Daniel  Tauvry  was  interesting,  however,  for  other  reasons.  He  was 
an  epigenesist,  and  wrote  vigorously  against  the  view  that  the  soul 
constructed  during  embryogeny  a  suitable  home  for  itself. 

Nine  years  later  two  books  appeared,  which  form  very  definite 
landmarks  in  the  history  of  embryology.  One  was  Martin  Schurig's 
Embryologia,  and  the  other  the  Elementa  Chymiae  of  Hermann  Boer- 

The  former,  however,  gave  to  the  world  no  new  experiments  or 
observations ;  it  was  the  first  of  what  we  should  now  call  the  typical 
"review"  kind  of  publication.  Schurig  saw  that  he  was  living  at 
the  end  of  a  great  scientific  movement  following  the  Renaissance, 
and  set  himself  accordingly  for  many  years  to  compile  large  treatises 
on  definite  and  restricted  subjects,  taking  care  to  give  all  references 
with  meticulous  accuracy,  and  to  omit  no  significant  or  insignificant 
work.  His  Spermatologia  was  the  first  to  appear  (in  1720),  and  it  was 
followed  in  1723  by  Sialologia  (on  the  saliva),  Chylologia  (1725), 
Muliebria  (1729),  Parthenologia  (1729),  Gynaecologia  (1731)  and  Haema- 
tologia  (1744).  His  Embryologia  was  the  last  but  one  of  the  series.  In 
it  he  treated  compendiously  of  all  the  theories  which  had  been 
advanced  about  embryology  during  the  immediately  preceding  two 
centuries,  and  his  chapters  on  foetal  nutrition  and  foetal  respiration 
throw  a  flood  of  light  on  to  the  "intellectual  climate"  in  which 
Harvey  and  Mayow  worked,  providing,  as  it  were,  the  perishable  back- 
ground of  their  immortal  thoughts.  Schurig's  bibliography  is  a  very 
striking  part  of  his  book,  extending  to  sixteen  pages,  and  including  five 
hundred  and  sixty  references;  it  was  the  first  attempt  of  its  kind. 

3-10.    Boerhaave,  Hamberger,  Mazin 

Hermann  Boerhaave  was  a  more  prominent  figure,  a  Professor  at 
Leyden  for  many  years,  and  renowned  for  his  encyclopaedic  learning 
on  all  subjects  remotely  connected  with  medicine.  His  Elementa 
Chymiae,  which  became  the  standard  chemical  book  of  the  whole 
period,  demonstrates  throughout  the  exceedingly  wide  outlook  of  its 


author,  and  contains  in  the  second  volume  what  must  be  regarded 
as  the  first  detailed  account  of  chemical  embryology.  I  reproduce 
here  the  relevant  passages  in  full  because  of  their  great  interest. 
It  will  be  noted  that  they  are  cast  in  the  form  of  lecture  addresses, 
as  if  they  had  been  taken  down  direct  from  the  lectures  of  the 
Professor,  a  fact  which  gives  them  a  peculiar  charm  when  it  is 
remembered  how  many  great  men  must  have  listened  to  them,  among 
them  Albrecht  von  Haller  and  Julien  de  la  Mettrie.  In  considering 
what  follows,  it  should  be  noted  that  Boerhaave's  interest  is  bio- 
logical all  the  time,  and  that  he  does  not  treat  the  liquids  of  the  egg, 
as  nearly  all  the  chemists  before  him  had  done,  as  substances  of 
curious  properties  indeed,  but  quite  remote  from  any  question  re- 
lating to  the  development  of  the  embryo.  Another  interesting  point 
is  that  he  deals  only  with  the  white,  and  hardly  mentions  the  yolk; 
this  is  perhaps  to  be  explained  by  the  Aristotelian  theory  that  the 
embryo  was  formed  out  of  the  white,  and  only  nourished  by  the 
yolk  {ex  alb 0  fieri,  ex  luteo  nutriri),  a  theory  which  was  still  alive,  in 
spite  of  Harvey,  in  the  first  half  of  the  eighteenth  century.  If  this 
was  what  was  at  the  bottom  of  Boerhaave's  mind,  then  it  is  obvious 
that  the  egg-white  would  be  to  him  the  liquid  inhabited  more  par- 
ticularly by  the  plastic  force.  This,  then,  is  what  he  has  to  say  about 
the  biochemistry  of  the  egg. 

Op.  Chem.  in  Animalia.  [Processus  log.]  The  albumen  of  a  fresh  egg  is  not 
acid,  nor  alkaline,  nor  does  it  contain  a  fermented  spirit.  The  white  of  a  fresh 
egg,  separated  from  the  shell,  the  membranes,  and  the  yolk,  I  enclose  in 
clean  glass  vessels,  and  into  each  of  these  I  pour  different  acids,  and  shake 
them  up,  mixing  them,  and  no  sign  of  ebullition  appears  however  I  treat 
them.  Therefore  I  lay  these  vessels  aside.  Now  in  these  other  two  vessels 
I  have  two  fresh  portions  of  albumen,  and  I  mix  with  them  in  one  case 
alkaline  salt  and  in  the  other  volatile  alkali.  You  see  they  are  quiet  without 
any  sign  of  effervescence.  Now  behold  a  remarkable  thing,  in  this  tall 
cylindrical  vessel  is  half  an  ounce  of  the  albumen  of  an  egg  and  two  drams 
of  spirits  of  nitre,  in  this  other  vessel  is  half  an  ounce  of  egg-white,  together 
with  four  and  a  half  ounces  of  oil  of  tartar  per  deliquium  both  heated 
up  to  92  degrees.  Pray  observe  and  behold,  with  one  movement  I  pour 
the  alkaline  albumen  into  the  acid  albumen,  with  what  fury  they  boil  up, 
into  what  space  they  rarefy  the  mass,  so  that  they  stream  out  of  the  vessel 
although  it  is  ten  pints  in  size  [decupli  capace] .  They  have  scarcely  changed 
their  colour.  But  when  the  effervescence  has  abated  how  suddenly  they 
return  to  the  limits  of  space  occupied  before.  But  now  if  more  egg-white 
is  heated  to  100  degrees  in  a  retort  [cucurbita]  an  insipid  water  containing 

i84  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

no  spirit  is  given  off.  If  egg-white  is  applied  to  the  naked  eye  or  naked 
nerve  it  does  not  give  the  smallest  sense  of  pain,  and  scarcely  affects  the 
smell;  nothing  more  inert  and  more  insipid  can  be  put  on  the  tongue.  It 
appears  mucous  and  viscid  to  the  touch,  not  at  all  penetrable.  Hence  in 
the  fresh  white  of  an  egg  there  is  no  alkali  or  acid,  or  both  together.  It  is 
indeed  a  thick,  sticky,  inert,  and  insipid  liquor,  yet  from  this  truly  vital 
liquid  at  a  heat  of  93  degrees  within  the  space  of  2 1  days  the  chick  grows 
in  the  incubated  egg  from  a  tiny  mass  hardly  weighing  a  hundredth  of  a 
grain  into  the  perfect  body  of  an  animal,  weighing  an  ounce  or  more. 
We  have  learnt  therefore  of  a  liquid  distinct  from  all  others,  from  which  by 
inscrutable  causes  fibres,  membranes,  vessels,  entrails,  muscles,  bones, 
cartilages,  and  all  the  other  parts,  tendons,  ligaments,  the  beak,  the  claws, 
the  feathers,  and  all  the  humours  can  be  produced — and  yet  in  this  liquid 
we  find  softness,  inertia,  absence  of  acid,  alkali,  and  spirit,  and  no  ten- 
dency to  effervesce.  Indeed,  if  there  were  the  slightest  effervescence  in  it, 
it  would  certainly  break  the  eggshell,  therefore  we  see  from  how  slow  and 
inactive  a  mass  all  the  solid  and  fluid  parts  of  the  chick  are  constructed. 
And  yet  this  itself  is  rendered  absolutely  useless  for  forming  the  chick  by 
greater  heat.  It  scarcely  bears  100  degrees  with  good  effect  but  at  a  less 
temperature  never  brings  forth  a  chick,  for  under  80  degrees  will  not 
suffice.  But  by  a  heat  kept  between  these  limits,  there  is  brought  about  so 
marvellous  an  attenuation  of  the  mucous  inactivity  that  it  can  exhale  a 
great  part  through  the  shell  of  the  egg  and  the  two  membranes,  the  yolk 
and  chalazae  alone  remaining  along  with  the  amniotic  sac.  For  the  yolk, 
the  uterine  placenta  of  the  chick,  takes  little  part  in  the  nourishment. 
Meanwhile  Malpighius  has  shown  that  this  albumen  is  not  a  liquid  of  a 
homogeneous  kind,  as  the  blood-serum  flowing  through  the  vital  vessels 
is,  but  that  it  is  a  structure  composed  of  numerous  membrane-like  and 
distinct  small  saccules,  filled  with  a  liquid  of  their  own,  in  the  same  way 
as  in  the  vitreous  humour  of  the  eye. 

[Processus  1 1 1 .]  Exploration  of  the  egg-white  with  alcohol.  In  this  trans- 
parent vessel  is  the  albumen  of  an  egg,  and  into  it,  as  you  perceive,  I 
gently  pour  the  purest  alcohol,  so  that  it  descends  down  the  sides  of  the 
vessel  and  reaches  the  albumen.  I  do  this  deliberately  and  with  such 
solicitude  that  you  may  see  the  surface  of  the  albumen  which,  touching 
the  alcohol,  holds  it  up,  being  immediately  coagulated,  while  the  lower 
part  remains  liquid  and  transparent.  As  I  now  gently  shake  them  together, 
it  appears  evident  that  wherever  the  alcohol  touches  the  albumen  a  con- 
cretion is  formed.  Behold  now,  while  I  shake  them  up  thoroughly  together, 
all  the  egg-white  is  coagulated.  If  alcohol  previously  warmed  is  employed 
in  this  experiment,  the  same  result  is  brought  about  but  more  rapidly. 
It  appears  therefore  that  the  purest  vegetable  spirits  immediately  coagulate 
the  plastic  and  nutrient  material. 

[Processus  112.]  The  fresh  albumen  of  an  egg  is  broken  up  by  distillation. 
These  fresh  eggs  have  been  cooked  in  pure  water  till  they  became  hard. 
I  now  take  the  shining  white,  separating  off  all  the  other  things,  and  break 
it  up  into  small  pieces.    I  put  these,  as  you  see,  into  a  clean  glass  retort 


[cucurbita]  and  I  duly  cover  it  by  fitting  on  an  alembic  and  add  a  receiver. 
By  the  rules  of  the  (chemical)  art  I  place  the  whole  retort  in  a  bath  of 
water  and  I  apply  to  it  successive  degrees  of  fire  until  the  whole  bath  is 
boiling.  No  vaporous  streaks  [^strid]  of  spirits  are  given  off  but  simple 
water  in  dewy  drops  and  this  in  incredible  quantity,  more  than  nine-tenths. 
I  continue  so  with  patience  until  by  the  heat  of  boiling  water  no  more 
drops  of  this  humour  are  given  off.  Then  this  water  shows  no  trace  of  oil, 
salt,  or  spirit ;  it  is  perfectly  transparent  and  tasteless,  except  that  it  eventu- 
ally grows  rather  sour.  It  is  odourless,  save  that  towards  the  end  it  gives 
off  a  slight  smell  of  burning.  It  shows  absolutely  no  sign  of  the  presence 
of  any  alkali,  when  I  test  it  in  every  way,  as  you  can  see  for  yourselves ; 
nor  does  it  reveal  any  trace  of  acid,  when  tried  how  you  will.  Here  you 
see  pounds  of  this  water,  but  in  the  bottom  of  the  now  open  retort  see, 
I  beg  of  you,  how  little  substance  remains.  Behold,  there  are  fragments 
contracted  into  a  very  small  space  in  comparison  with  the  former  quantity. 
They  are  endowed  with  a  golden  yellow  colour,  especially  where  they  have 
touched  the  glass,  but  yet  they  are  transparent  after  the  manner  of  coloured 
glass.  When  I  take  them  out  I  find  them  very  light,  very  hard,  quite  fragile, 
and  breaking  apart  with  a  crack,  smelling  slightly  of  empyreuma,  with 
a  taste  rather  bitter  from  the  fire,  and  without  any  flavour  of  alkali  or 
acid.  This  is  the  first  part  of  the  analysis.  Now  I  take  these  remaining 
fragments  in  a  glass  retort  [retortam]  in  such  a  way  that  two-thirds  remain 
over.  I  put  the  retort  into  a  stove  of  sand,  first  arranging  a  large  receiver. 
Then  thoroughly  luting  all  the  joints  I  distil  by  successive  grades  of  fire 
and  finally  by  the  highest  which  I  call  suppressionis.  There  ascends  a  spirit, 
running  in  streaks  [^striatim]  fat  and  oily,  and  at  the  same  time,  volatile 
salts  of  solid  form  everywhere  on  the  walls  of  the  vessel,  rather  plentiful 
in  proportion  to  the  dried  fragments  but  small  in  proportion  to  the  whole 
albumen  before  the  water  had  been  removed  from  it.  Finally  an  oil  appears 
besides  the  light  golden  material  mixed  with  the  first,  black,  thick,  and 
pitchy.  When  by  the  extreme  force  of  the  fire  this  oil  is  finally  driven  forth, 
then  the  earth  in  the  bottom,  closely  united  with  its  most  tenacious  oil, 
swells  up  and  is  rarefied  and  rises  right  up  to  the  neck  of  the  retort  so  that 
had  the  retort  been  overfull  it  would  have  entered  into  the  neck  and 
clogged  it  up,  even  causing  it  to  burst,  with  danger  to  the  bystanders.  The 
operation  is  to  be  continued  till  no  more  comes  out.  That  first  spirit,  oily 
and  fatty,  is  clearly  alkaline  by  every  test,  as  you  may  tell  from  the  way  it 
effervesces  when  acid  is  poured  on  it.  If  we  rectify  it  we  resolve  it  into 
an  alkaline  volatile  salt,  an  oil,  and  inert  foetid  water.  The  salt  fixed  to 
the  walls  is  completely  alkaline,  sharp,  fiery,  oily,  and  volatile;  and  the 
final  oil  is  specially  sharp,  caustic,  and  foetid.  The  black  earth  which 
remains  in  the  retort  is  shiny,  light,  thin,  and  fragile,  foetid  from  the  final 
empyreumatic  oil,  and  soft  because  of  it.  If  then  it  is  burnt  on  an  open 
fire,  it  leaves  a  little  fixed  earth  which  is  white,  insipid,  tasteless,  and 
odourless,  from  which  scarcely  any  salt  can  be  extracted,  but  only  a  very 
heavy  dusty  powder  \^pollinein\. 

Cf.  the  dry  distillation  of  egg-white  by  Pictet  &  Cramer  in  1919. 

i86  EMBRYOLOGY   IN  THE   SEVENTEENTH        [pt.  ii 

[Processus  113.]  The  fresh  albumen  of  an  egg  will  putrefy.  Sound  eggs  kept 
at  70°  for  some  days  will  become  foetid  and  stink. . .  .We  have  learnt  then 
that  this  is  the  nature  of  the  material  which  will  shortly  be  changed  into 
the  structure,  form,  and  all  the  parts  of  the  animal  body.  Repose  and  a 
certain  degree  of  heat  produce  that  effect  in  that  material.  We  observe 
therefore  the  spontaneous  corruption  and  change  of  the  material,  and  what 
is  extremely  remarkable,  if  an  impregnated  egg  is  warmed  in  an  oven  [in 
hypocaustis]  to  a  heat  of  92  degrees  it  employs  these  attenuated  parts 
changed  by  such  a  heat  to  nourish,  increase,  and  complete  the  chick  for 
21  days.  But  in  this  chick  nothing  alkaline,  foetid,  or  putrid  is  found, 
hence  observe,  O  doctors  [medici] ,  the  remarkable  manifestations  of  nature 
^by  repose  and  a  certain  degree  of  heat  a  thick  substance  becomes  thin, 
a  viscous  substance  becomes  liquid,  an  odourless  substance  becomes  foetid, 
an  insipid  substance  becomes  sour  and  extremely  acrid  and  bitter  to  the 
taste,  a  soothing  substance  becomes  caustic,  a  non-alkali  becomes  alkaline, 
a  latent  oil  becomes  sweet  and  putrid.  Let  these  results  be  compared  with 
the  observations  of  Marcellus  Malpighius  on  the  incubated  egg,  and  we 
shall  observe  things  which  shall  surprise  us.  I  took  care  to  investigate  only 
the  albumen  of  the  egg  first  of  all,  separating  the  other  parts  off  where 
possible,  for  the  albumen  alone  forms  the  whole  of  the  material  which 
proceeds  to  feed  [in  pabulum]  the  embryo.  The  other  constituents  of  the 
egg  only  assist  in  changing  the  albumen,  so  that  when  it  is  changed,  it 
miay  be  applied  to  forming  the  structure  of  the  chick. 

Boerhaave's  treatment  of  these  subjects  has  only  to  be  compared 
with  that  of  Joachim  Beccher,  who  wrote  in  1 703,  to  show  how 
thoroughly  modern  in  outlook  it  is.  Beccher's  Physica  Subterranea 
contains  a  whole  section  devoted  to  the  growth  of  the  embryo,  but 
it  is  extremely  confused  and  very  alchemical  in  its  details.  The 
advance  made  in  the  thirty  years  between  Beccher  and  Boerhaave 
was  immense,  but,  if  the  biochemistry  of  development  advanced  so 
fast,  its  biophysics  was  not  far  behind,  as  is  shown  by  the  work  of 
G.  E.  Hamberger  and  J.  B.  Mazin. 

Hamberger's  most  important  contributions,  contained  in  his  Physio- 
logia  medica  of  1 75 1 ,  were  his  quantitative  observations  on  the  water- 
content  of  the  embryo  and  its  growth-rate,  in  which  he  had  no  fore- 
runners, Hamberger  showed  "that  there  are  much  less  solid  parts 
in  the  foetus  than  in  the  adult.  The  cortical  substance  of  the  brain  of 
an  embryo  loses  8694  parts  in  10,000  on  drying  but  in  the  adult  it  only 
loses  8096  and  that  of  the  cerebellum  from  81  parts  is  reduced  to  12. 
The  maxillary  glands  of  the  embryo  lose  out  of  10,000  parts  8469,  the 
liver  8047,  the  pancreas  7863,  the  arteries  8278  and  even  the  cartilages 
lose  four-fifths  of  their  weight,  decreasing  from  10,000  to  8149I ".  The 


corresponding  figures  for  the  adult  were:  liver  7192,  and  heart  7836. 
These  figures  do  not  widely  diflfer  fi:-om  those  obtained  in  recent  times. 

J.  B,  Mazin  published  his  Conjecturae  physico-medico-hydrostaticae  de 
respiratione  foetus  in  1737  and  his  Tractatus  medico-mechanica  in  1742. 
In  the  first  of  these  works  Mazin  supports  what  is  essentially  Mayow's 
theory  of  embryonic  respiration,  without,  however,  mentioning 
Mayow  more  than  once.  It  had  not  been  popular  since  1700,  though 
Pitcairn  had  defended  it.  Mazin  put  the  liquids  of  eggs  under  an 
air-pump,  and  observing  that  air  could  be  extracted  from  them 
affirmed  that  the  air  was  hidden  in  them  and  that  the  embryo  could 
therefore  respire.  He  spoke  of  "aerial  particles"  in  the  amniotic 
liquid,  and  discussed  the  respiration  of  fishes  in  connection  with  this. 
The  specific  gravity  of  the  embryo  also  interested  him,  and  he  did 
a  great  deal  of  calculation  and  experiment  on  it.  His  most  interesting 
passage,  perhaps,  is  that  in  which  he  mentions  the  "Eolipile"  of 
the  Alexandrians,  the  primitive  form  of  the  steam-engine,  and  says 
that  just  as  the  heat  of  the  fire  makes  the  water  boil,  so  the  heat  of 
the  viscera  makes  the  amniotic  liquid  boil,  giving  off  respirable 
vapours.  The  time-relations  of  this  analogy  are  interesting,  for  in 
1705  Thomas  Newcomen  had  succeeded  in  making  a  steam-engine 
which  worked  with  considerable  precision,  and  the  question  of  steam- 
power  was  widely  discussed.  Possibly  Mazin  was  acquainted  with 
the  Marquis  of  Worcester's  Century  of  the  Names  and  Scantlings  oj 
Inventions,  which  had  been  published  in  1663,  and  which  had  con- 
tained an  aeolipile  or  "water-commanding  machine".  England  was 
the  centre  of  this  movement  and  other  countries  employed  English- 
men as  engineers;  Humphrey  Potter,  for  instance,  erected  a  steam- 
engine  for  pumping  at  a  Hungarian  mine  in  1 720. 

As  for  the  discovery  of  oxygen,  it  was  near  at  hand,  and  Scheele  in 
1 773  and  Priestley  in  1 774  were  soon  to  supply  the  knowledge  without 
which  Mazin  could  not  proceed  further. 

In  his  second  book,  Mazin  reported  many  quantitative  observations 
on  the  specific  gravity  of  the  embryo.  He  found  that  it  diminished 
as  development  proceeded,  being  to  the  amniotic  liquid  as  282  to 
274  in  the  fourth  month  and  as  504  to  494  in  the  fifth  month. 

Another  instance  of  the  way  in  which  experimental  physical  ques- 
tions now  began  to  come  in  is  afforded  by  the  work  of  Joseph  Onymos, 
whose  De  Matura  Foetu  of  1 745  spoke  of  the  specific  gravity  of  the 
embryo  at  different  stages  of  development. 

i88  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

These  writers,  together  with  Haller  himself,  and  J.  C.  Heffter 
who  handled  problems  of  embryonic  rate  of  growth  contribute  to 
one  of  the  best,  because  most  quantitative,  aspects  of  eighteenth- 
century  embryology. 

3*11.    Albrecht  von  Haller  and  his  Contemporaries 

Boerhaave's  greatest  pupil  was  Albrecht  von  Haller.  Like  O.  W. 
Holmes,  at  Harvard,  Haller  occupied  a  "settee"  rather  than  a  "chair", 
at  Gottingen,  and  taught  not  only  physiology  but  also  medicine 
and  surgery,  botany,  anatomy  and  pharmacology.  Nor  did  he 
merely  deal  with  so  many  subjects  superficially;  in  each  case  he 
published  what  amounted  to  the  best  and  most  complete  text-book 
up  to  then  written.  Haller  was  made  Professor  in  1736,  and  for 
many  years  worked  at  Gottingen,  devoting  much  of  his  time  to 
embryological  researches,  which,  with  those  of  his  opponent  Wolff, 
stand  out  as  the  greatest  between  Malpighi  and  von  Baer.  In  1 750 
he  published  a  series  of  dissertations  and  short  papers  on  all  kinds 
of  physiological  subjects,  which  would  have  been  the  direct  ancestors 
of  the  modern  compilations  of  groups  of  experts,  had  they  been  more 
systematically  arranged.  The  volume  on  generation  repays  some 
study.  The  contributions  relevant  to  the  present  discussion  had  been 
written  at  various  times  during  the  previous  seventy  years,  and  may 
be  summarised  as  follows : 

IV.  Christopher  Sturmius,  De  plantarum  animaliumque  generatione. 
(First  published  1687.)  In  this  paper  Sturmius  argues  on 
behalf  of  the  preformation  theory  "which  in  our  times 
does  not  lack  supporters",  quoting  Perrault,  Harvey  and 
Descartes.  He  contents  himself  with  countering  arguments 
which  had  been  urged  against  it,  as,  {a)  spontaneous 
generation,  {b)  annual  recurrence  of  plants,  {c)  insect 
metamorphosis,  {d)  generation  without  copulation. 
V.  Rudolf  Jacob  Camerarius,  Specimen  experimentorum  physiologico- 
therapeuticorum  circa  generationem  hominis  et  animalium.  The 
most  interesting  thing  about  this  is  that  Camerarius 
mentions  the  observations  of  D.  Seiller,  a  sculptor,  who 
had  ascertained  that  the  body  is  five  times  the  size  of  the 
head  in  the  embryo  but  seven  and  a  half  times  the  size  of  it 
in  the  adult.  This  is  in  the  direct  line  between  Leonardo 
and  Scammon. 

SECT.  3] 



XV.   Philip  Gravel,  De  Super Joetatione.    (First  published  1738.) 

XVIII.  Adam  Brendel,  De  embryone  in  ovulo  ante  conceptum praeexistante. 
(First  published  1703.)  Brendel  "stands  for  the  Graafian 
hypothesis''.  Unfortunately,  he  was  also  a  preformationist 
and  believed  that  every  limb,  organ,  and  function  existed 
not  potentially  but  actually  in  the  unfertilised  Qgg  before 
its  passage  down  the  Fallopian  tube. 

XXII.  Camillus  Falconnet,  Non  est  fetui  sanguis  maternus  alimento. 
(First  published  171 1.)  This  is  the  first  of  the  French 
contributions  to  the  book;  they  are  all  very  markedly 
shorter  than  the  German  ones  and  much  less  heavily 
ornamented  with  irrelevant  quotations.  Falconnet  is  con- 
cerned to  prove  that  the  maternal  and  foetal  circulations 
are  separate,  and  he  describes  in  an  admirably  concise 
manner  an  experiment  in  which  he  bled  a  female  dog  to 
death,  after  which,  opening  the  uterus,  he  discovered  that 
the  embryonic  blood-vessels  were  full  of  blood  although 
those  of  the  mother  had  none  in  at  all.  Arantius  was  there- 
fore justified.    Falconnet  was  soon  confirmed  by  Nunn. 

XXIII.  Jean  de  Diest's  Sui  Sanguinis  solus  opifex  fetus  est  (first 
published  1735)  was  written  to  prove  a  similar  point.  He 
refers  to  the  experiment  of  Falconnet  and  the  injections 
of  F.  Hoffmann,  and  criticises  Cowper's  experiment  in 
which  mercury  had  been  injected  into  the  umbilical  vessels 
and  found  in  the  maternal  circulation,  on  the  grounds  that 
mercury  is  so  "tenuous  and  voluble"  that  it  might  pass 
where  blood  could  not  pass  normally.  He  also  objects  to 
the  view  that  the  foetus  is  nourished  by  the  amniotic  liquid. 

XXIV.  Francis  David  Herissant,  Secundinae  fetui  pulmonis  praestant 
officia,  et  sanguine  materno  fetum  non  alitur.  (First  published  in 
1 741.)  An  excellent  paper,  in  which  the  respiratory  function 
of  the  placenta  is  proved  by  the  observation  that  the  foetal 
blood-vessel  leading  to  the  placenta  is  always  full  of  dark 
venous  blood,  while  that  leading  away  fi-om  the  placenta 
is  light  and  arterial  [floridiori  coccineoque  colore,  ut  ipsemet 
observavi].  Herissant  adduces  also  the  cases  of  acephalic 
monsters,  such  as  that  of  Brady,  which  could  not  possibly 
have  drunk  up  any  amniotic  fluid,  and  yet  were  fully  formed 

igo  THE   EIGHTEENTH   CENTURY  [pt.  ii 

in  all  other  respects.  He  concludes  that  the  umbilical  cord 
serves  for  respiration  and  nutrition. 

XXV.  After  these  three  French  workers,  there  is  a  great  drop  to 
Johannes  Zeller,  whose  Infanticidas  non  absolvit  nee  a  tortura 
liberal  pulmonum  infantis  in  aqua  subsidentia   (first  published 

1 691)  is  a  long-winded  discussion  of  the  floating  lung  test 
in  forensic  medicine.  His  memory  deserves  a  word  of  obloquy 
for  his  vigorous  insistence  upon  torture  and  death  for  in- 
fanticide even  during  puerperal  insanity.  Perhaps  it  was 
Zeller  who  called  forth  the  noble  answer  of  de  la  Mettrie 
to  this  inhumanity  in  his  Man  a  Machine. 

XXVI.   Zeller's  De   Vila   Humana  ex  June  pendenle  (first   published 

1692)  is  no  better,  though  at  the  time,  perhaps  because 
of  its  striking  title,  it  was  famous.  It  deals  with  the  ligation 
of  the  umbilical  cord  at  birth. 

This  completes  the  list  of  the  papers  published  by  Haller  in  his 
1750  collection.  He  retired  from  the  Gottingen  chair  three  years 
later,  and  in  1757  the  first  volume  of  his  Elemenla  Physiologiae  was 
published,  probably  the  greatest  text-book  of  physiology  ever  written. 
It  appeared  only  by  slow  degrees,  so  that  it  was  not  until  1766  that 
the  embryological  section  was  available.  This  volume  contains 
a  discussion  of  a  mass  of  literature,  most  of  which  had  arisen 
during  the  preceding  twenty-five  years,  for,  although  many  of  the 
names  mentioned  by  Haller  occur  also  in  Schurig,  yet  many  are 
quite  new. 

Haller  himself  published  in  1 767  a  volume  of  his  collected  papers 
on  embryology,  most  of  which  were  concerned  with  the  developing 
heart  of  the  chick,  which  he  worked  out  very  thoroughly,  in  collabora- 
tion with  Kuhlemann.  (Kuhlemann  had  already  done  for  the 
sheep  what  Harvey  had  done  for  the  doe.)  He  made  a  beginning 
with  the  quantitative  description  of  embryogeny,  and  one  of  his 
tables  showing  the  changing  lengths  of  the  bones  is  reproduced  here- 
with (Fig.  10).  He  was  a  convinced  preformationist,  a  fact  which  was 
largely  due  to  his  researches  on  the  hen's  egg,  where  he  observed  that 
the  yolk  had  a  much  more  intimate  connection  with  the  embryo 
than  had  previously  been  supposed.  Since  the  whole  yolk  was  part  of 
the  embryo,  as  it  were,  the  preformation  theory  seemed  to  him  to 
fit  the  facts  better  than  epigenesis. 












Quart  us 






l|     MUS 



MUS  Se- 









1 8-  prox. 










+4.  ptox. 





















1 1 



43.  prox 










3  0.  prox. 























Fig.  10.   Facsimile  of  a  table  in  A.  von  Haller's  Elementa  Physiologiae  of  1766,  containing  some  of  his 
observations  on  the  growth  in  length  and  weight  of  embryonic  bones  in  the  chick. 

192  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

Haller  went  further  than  Schurig,  in  that  he  usually  gave  an  opinion 
of  his  own  after  summarising  those  of  other  people,  but  his  views  were 
by  no  means  always  enlightened,  and  the  atmosphere  of  Buffon  is, 
on  the  whole,  more  congenial  to  us  than  that  of  Haller.  Haller, 
for  example,  believed  that  the  amniotic  liquid  had  nutritious  pro- 
perties, and  that  the  nutrition  of  the  embryo  in  mammalia  was 
accomplished  first  of^  all  per  os  and  afterwards  per  umbilicum.  He  denied 
that  the  placenta  had  any  respiratory  function,  and,  indeed,  his 
whole  teaching  on  respiration  was  retrograde.  He  mentions,  how- 
ever, an  experiment  of  Nicolas  Lemery's,  in  which  it  had  been 
found  that  indigo  would  penetrate  the  shell  of  a  developing  hen's 
tgg  from  the  outside.  Consequently,  air  might  do  so  too,  and 
Vallisneri  had  shown  that,  if  an  egg  was  placed  in  boiled  water  under 
an  air-pump,  the  air  inside  would  rush  out  through  the  shell  and 
appear  in  the  form  of  bubbles. 

Haller  was  much  more  progressive  in  holding  the  origin  of  the 
amniotic  liquid  (according  to  him  a  subject  of  extraordinary  diffi- 
culty— " solutionem  non  promittam'")  to  be  a  transudation  from  the 
maternal  blood-vessels.  He  followed  Noortwyck  in  asserting  the 
separateness  of  the  maternal  and  foetal  circulations  in  mammalia. 
He  opposed  the  existence  of  eggs  in  vivipara — "We  may  conclude 
from  all  this",  he  said,  "that  the  ovarian  vesicles  are  not  eggs  and 
that  they  do  not  contain  the  rudiments  of  the  new  animal".  But  he 
accepted  it  in  the  restricted  sense  that  the  embryonic  membranes 
resembled  an  egg,  thus:  "If  we  call  an  egg  a  hollow  membranous 
pocket  full  of  a  humour  in  which  the  embryo  swims,  we  may  admit 
the  opinion  of  the  older  authors  who  derive  all  animals  from  eggs 
with  the  exception  of  the  tiny  simple  animals  of  which  we  have 
already  spoken.  It  was  in  this  sense  that  Aristotle  and  Empedocles 
before  him,  said  that  even  trees  were  oviparous.  This  has  also  been 
confirmed  by  the  experiments  of  Harvey  on  insects,  fishes,  birds,  and 

Haller's  most  original  work  was  in  connection  with  the  growth- 
rate  of  the  embryo ;  here  he  struck  out,  for  once,  into  entirely  new 
country.  "The  growth  of  the  embryo  in  the  uterus  of  the  mother  is 
almost  unbelieveably  rapid.  We  do  not  know  what  its  size  is  at  the 
moment  of  its  formation,  but  it  is  certainly  so  small  that  it  cannot 
be  seen  even  with  the  aid  of  the  best  microscopes,  and  it  reaches  in 
nine  months  the  weight  of  ten  or  twelve  pounds.    In  order  to  clear 


up  this  speculation,  let  us  examine  the  growth  of  the  chick  in  the 
egg.  We  cannot  in  this  case  either  measure  its  size  at  the  moment 
when  the  egg  is  put  to  incubate  but  it  cannot  be  more  than  j^  in. 
long,  for  if  it  were,  it  would  be  visible,  and  yet  25  days  later  it  is 
4  ins,  long.  Its  relation  is  therefore  as  64  to  64  millions  or  i  to  i 
million.  This  growth  takes  place  in  a  singular  manner,  it  is  very  rapid 
in  the  beginning  and  continually  diminishes  in  speed.  The  growth 
on  the  first  day  is  from  i  to  gi^^  and  what  Swammerdam  calls  a 
worm  grows  in  one  day  from  one-twentieth  or  one-thirtieth  of  a 
grain  to  seven  grains,  i.e.  it  increases  its  weight  by  140  or  240  times. 
On  the  second  day  the  growth  of  the  chick  is  from  i  to  5,  on  the  third 
day,  from  i  to  not  quite  4,  on  the  fifth  day  from  i  to  something 
less  than  3.  Then  from  the  sixth  to  the  twelfth  day,  the  growth  each 
day  is  hardly  from  4  to  5,  and  on  the  twenty-first  day  it  is  about 
from  5  to  6.  After  the  chick  has  hatched,  it  grows  each  day  for  the 
first  40  days  at  an  approximately  constant  rate,  from  20  to  2 1  on  each 
day.  The  increase  of  the  first  twenty-four  hours  is  therefore  in  relation 
to  that  of  the  last  twenty-four  hours  as  546I  to  5  or  145  to  i.  Now 
as  the  total  increase  in  weight  in  the  egg  is  to  that  of  the  whole 
growth  period  (up  to  the  adult)  as  2  to  24  ozs.,  all  the  post-embryonic 
growth  is  as  i  to  12,  i.e.  it  is  to  the  growth  of  one  day  alone  early 
in  incubation  as  i  to  7|.. .  .The  growth  of  man,  like  that  of  the 
chick,  decreases  in  rapidity  as  it  advances.  Let  us  suppose  that  a 
man,  at  the  instant  of  conception,  weighs  a  hundred-thousandth  of 
a  grain  and  that  a  one-month  old  embryo  weighs  30  grains;  then 
the  man  will  have  acquired  in  that  time  more  than  300,000  times 
the  weight  that  he  had  to  begin  with.  But  if  a  foetus  of  the  second 
month  weighs  3  ozs.  as  it  approximately  does,  he  will  only  now  have 
acquired  48  times  the  weight  he  had  at  the  beginning  of  the  period. 
This  is  a  prodigious  decrease  in  speed,  and  at  the  end  of  the  ninth 
month  he  will  not  weigh  more  than  about  105  ozs.,  which  is  not 
more  than  an  average  increase  of  15  per  month.  A  child  three  years 
old  is  about  half  the  size  of  an  adult.  If  then  the  adult  weighs 
2250  ozs.  the  three-year  old  child  only  weighs  281  ozs.,  which  is  an 
eighth  of  the  adult  weight.  Now  from  birth  to  3  years  he  will  grow 
from  105  to  281  or  as  5  to  14,  but  in  the  following  22  years  he  will 
only  accumulate  2250  ozs.  or  eight  times  what  he  had  at  3  years. 
The  growth  of  a  man  will  therefore  be  in  the  first  month  of  intra- 
uterine life  as  I  to  300,000,  in  the  second  as  i  to  48,  in  each  of  the 

N  E  I  13 

194  EMBRYOLOGY   IN  THE   SEVENTEENTH       [pt.  ii 

others  as  i  to  15.  In  the  first  3  years  of  extra-uterine  life  his  growth 
will  be  from  164  to  281  and  in  the  succeeding  22  years  from  281  to 
384,  and  the  growth  of  the  first  month  to  the  last  will  be  as  300,000 
to  ^%  or  136,800,000  to  28,  or  4,885,717  to  i.  The  whole  growth  of 
man  will  consequently  be  as  108,000,000  to  i." 

In  spite  of  the  rather  unfamiliar  language  in  which  these  facts  are 
described,  and  the  theory  of  the  growth  of  the  heart  which  Haller 
subsequently  put  forth  to  explain  them,  they  remain  fundamental 
to  embryology.  Their  quantitative  tone  is  indeed  remarkably  modern. 
In  my  opinion,  when  all  the  voluminous  writings  of  Haller  are  care- 
fully searched  through,  nothing  more  progressive  and  valuable  than 
these  figures  can  be  found.  Haller  and  Hamberger  stand  thus 
between  Leonardo  on  the  one  hand  and  Minot  and  Brody  on  the 
other.  That  they  stood  so  much  alone  is  only  another  indication  of 
the  extraordinary  reluctance  with  which  the  men  of  past  generations 
assented  to  the  truth  contained  in  Robert  Mayer's  immortal  words, 
"Eine  einzige  Zahl  hat  mehr  wahren  und  bleibenden  Wert  als  eine 
kostbare  Bibliothek  von  Hypothesen". 

Of  development  as  a  whole,  Haller  spoke  thus,  "  In  the  body  of  the 
animal  therefore,  no  part  is  made  before  any  other  part,  but  all  are 
formed  at  the  same  time.  If  certain  authors  have  said  that  the  animal 
begins  to  be  formed  by  the  backbone,  by  the  brain,  or  by  the  heart,  if 
Galen  taught  that  it  was  the  liver  which  was  first  formed,  if  others  have 
said  that  it  was  the  belly  and  the  head,  or  the  spinal  marrow  with  the 
brain,  adding  that  these  parts  make  others  in  turn,  I  think  that  all  these 
authors  only  meant  that  the  heart  and  the  brain  or  whatever  organ 
it  was,  were  visible  when  none  of  the  other  parts  yet  were,  and  that 
certain  parts  of  the  embryonic  body  are  well  enough  developed  in  the 
first  few  days  to  be  seen  while  others  are  not  so  until  the  latter  part  of 
development;  and  others  again  not  till  after  birth,  such  as  the  beard 
in  man,  the  antlers  in  the  stag,  the  breasts  and  the  second  set  of  teeth. 
If  Harvey  thought  he  descried  an  epigenetic  development,  it  was 
because  he  saw  first  a  little  cloud,  then  the  rudiments  of  the  head,  with 
the  eyes  bigger  than  the  whole  body,  and  little  by  little  the  viscera 
being  formed.  If  one  compares  his  description  with  mine,  one  will  see 
that  his  description  of  the  development  of  the  deer  corresponds 
exactly  with  mine  of  the  development  of  the  chick.  If,  more  than 
twenty  years  ago,  before  I  had  made  many  observations  upon  eggs 
and  the  females  of  quadrupeds  I  employed  this  reasoning  to  prove 


that  there  is  a  great  difference  between  the  foetus  and  the  perfect 
animal,  and  if  I  said  that  in  the  animal  at  the  moment  of  conception 
one  does  not  find  the  same  parts  as  in  the  perfect  animal,  I  have 
realised  abundantly  since  then  that  all  I  said  against  preformation 
really  went  to  support  it".  The  reasons  for  this  change  of  opinion 
become  no  clearer  as  Haller's  writings  are  more  assiduously  read, 
and,  as  Dareste  says,  why  he  should  have  made  it,  will  always 
remain  a  mystery. 

The  emboitement  aspect  of  preformation  presented  no  difficulties  to 
Haller.  "It  follows",  he  said,  speaking  of  the  generation  of  Volvox, 
"that  the  ovary  of  an  ancestress  will  contain  not  only  her  daughter, 
but  also  her  granddaughter,  her  great-granddaughter  and  her  great- 
great-granddaughter,  and  if  it  is  once  proved  that  an  ovary  can 
contain  many  generations,  there  is  no  absurdity  in  saying  that  it 
contains  them  all," 

The  following  passage  is  interesting.  "We  must  proceed  to  say 
what  is  the  efficient  cause  of  the  beautiful  machine  which  we  call 
an  animal.  First  of  all  let  us  not  attribute  it  to  chance,  as  Ofrai 
[is  this  Julien  Offi-ay  de  la  Mettrie?  Haller  had  a  habit  of  using 
Christian  names,  e,g,  Turberville  for  J.  T.  Needham]  would  have 
us  do,  for  although  he  pretends  that  all  animals  come  from  earth, 
he  is  not  attached  to  the  ancient  opinion,  and  nobody  now  believes 
what  Aelian  says,  namely  that  frogs  are  born  from  mud. .  . ,  Vallisneri 
has  found  the  fathers  and  mothers  of  the  little  worms  in  galls,  a  quest 
of  which  Redi  despaired,  and  Redi  in  his  turn  has  made  with  exacti- 
tude and  precision  those  experiments  which  Bonannus,  Triumphet, 
and  Honoratus  Faber  had  only  sketched  out  imperfectly.  Moreover, 
no  seed,  no  clover. .  .  .  This  was  the  received  opinion  but  in  our  century 
a  proscribed  notion  has  been  revivified  and  some  great  men  have 
pretended  that  there  are  little  animals  which  are  engendered  by  an 
equivocal  generation,  without  father  and  mother,  and  that  all  the 
viscera  and  all  the  parts  of  these  animals  do  not  exist  together,  but 
that  the  nobler  parts  are  formed  first  by  epigenesis  and  that  then 
the  others  are  formed  little  by  little  afterwards."  This  is  an  admirable 
illustration  of  how  spontaneous  generation  and  epigenesis  were  bound 
up  together,  "M.  Needham",  Haller  goes  on  to  say,  "does  not  admit 
an  equivocal  generation  but  he  does  admit  epigenesis,  and  a  corporeal 
non-intelligent  force,  which  constructs  a  body  from  a  tiny  little  germ 
furnishing  the  necessary  matter  for  it.    He  says  that  there  are  only 


196  EMBRYOLOGY   IN   THE   SEVENTEENTH        [pt.  11 

the  primitive  germs  which  were  made  at  the  original  creation  and 
that  germs  organised  Hke  animals  do  by  no  means  pre-exist,  for  if 
they  did,  molae  uterinae,  encysted  tumours,  and  the  like,  could  not 
come  into  being."  Haller  then  goes  on  to  describe  Needham's 
experiments  with  meat  broths,  etc.,  and  objects  to  his  "system", 
largely  on  the  ground  that  "blind  forces  without  any  intelligence 
could  hardly  be  able  to  form  animals  for  ends  foreseen  and  ready 
to  take  their  places  in  the  scheme  of  beings".  He  considers  that 
Needham's  theories  are  completely  disproved  by  experiments  such 
as  those  of  Spallanzani,  though,  curiously  enough,  he  does  not  quote 
the  latter  author  in  this  connection.   I  shall  return  to  this  later. 

"Nobody",  he  goes  on  to  say,  "has  upheld  epigenesis  more  than 
M.  Wolff,  who  has  undertaken  an  examination  to  demonstrate  that 
plants  and  animals  are  formed  without  a  mould  out  of  matter  by  a 
certain  constant  force  which  he  calls  'essential'  [in  his  Theoria 
Generationis] ....  I  have  indeed  seen  many  of  the  phenomena  which 
he  describes,  and  it  is  certain  that  the  heart  seems  to  be  formed  out 
of  a  congealed  humour  and  that  the  whole  animal  appears  to  have 
the  same  consistency.  But  it  does  not  follow  that  because  this 
primitive  glue  which  is  to  take  on  the  shape  of  the  animal  does  not 
appear  to  possess  its  structure  and  all  its  parts,  it  has  not  effectively 
got  them.  I  have  often  given  greater  solidity  to  this  jelly  by  the  use 
merely  of  spirits  of  wine  and  by  this  means  I  saw  that  what  had 
appeared  to  me  to  be  a  homogeneous  jelly  was  composed  of  fibres, 
vessels,  and  viscera.  Now  surely  nobody  will  say  that  the  vis 
essentialis  of  the  spirit  of  wine  gave  an  organic  structure  to  an  un- 
formed matter,  on  the  contrary  it  is  rather  in  the  removal  of  trans- 
parency and  the  accession  of  greater  firmness  to  the  extremities,  as 
well  as  the  making  of  a  more  obvious  boundary  to  the  contour  of 
a  viscus  that  one  could  see  the  structure  of  a  cellular  tissue,  which 
was  ready  to  be  formed  but  which  the  transparency  had  previously 
hidden  and  the  wetness  not  allowed  to  be  circumscribed  by  lines. .  .  . 
Finally,  to  cut  a  long  story  short,  why  does  this  vis  essentialis, 
which  is  one  only,  form  always  and  in  the  same  places  the  parts  of 
an  animal  which  are  so  different,  and  always  upon  the  same  model, 
if  inorganic  matter  is  susceptible  of  changes  and  is  capable  of  taking 
all  sorts  of  forms?  Why  should  the  material  coming  from  a  hen 
always  give  rise  to  a  chicken,  and  that  from  a  peacock  give  rise  to 
a  peacock?    To  these  questions  no  answer  is  given."  This  was  the 


case  because  Wolff  was  not  a  theorist,  but  rather  an  experimentalist; 
his  writings  are  marked  by  their  abstention  from  the  discussion  of 
speculative  points.  The  above  passage  is  very  interesting.  It  reminds 
us  of  the  great  difficulties  with  which  the  embryologists  of  this  epoch 
had  to  contend.  Serial  section  cutting  was  unknown,  the  staining 
of  thin  layers  and  reconstruction  were  unheard  of;  even  the  hardening 
of  the  soft  embryonic  tissues  was  only  just  discovered,  as  is  indicated 
by  Haller  above.  Hertwig  has  excellently  discussed  the  advances  in 
embryological  technique  which  took  place  during  this  and  the  fol- 
lowing century.  It  is  true  that  dyes  were  beginning  to  be  used,  as 
some  instances  already  given  demonstrate,  and  as  is  seen  from  the  use 
of  madder  in  the  staining  of  bones,  which  began  about  this  time,  and 
was  later  much  used  by  the  Hunters.  Heertodt's  Crocologia  is  im- 
portant in  this  connection.  Heertodt,  by  injecting  saffron  into  the 
maternal  circulation,  found  it  afterwards  in  the  amniotic  fluid,  and 
his  experiment  was  cited  by  Haller  in  support  of  that  theory  of  the 
origin  of  the  liquid.  But  the  most  important  advance  in  technique 
was  the  progress  in  artificial  incubation.  The  art,  though  lost  through- 
out the  Middle  Ages  and  the  seventeenth  century,  was  now  to  be 

During  this  period  much  work  was  done  on  it.  As  far  back  as 
1 600,  de  Serres  had  mentioned  some  experiments  of  this  nature,  but 
they  were  not  successful.  "The  chicks",  he  said,  "were  usually  born 
deformed,  defective  or  having  too  many  legs,  wings,  or  heads,  nature 
being  inimitable  by  art."  Birch,  in  his  History  of  the  Royal  Society,  also 
refers  to  it.  "Sir  Christopher  Heydon  [a  relative  of  Digby's  Sir 
John?]  together  with  Drebell,  long  since  in  the  Minories  hatched 
several  hundred  eggs  but  it  had  this  effect,  that  most  of  the  chickens 
produced  that  way  were  lame  and  defective  in  some  part  or  other." 
Antonelli  states  that  similar  trials  were  made  at  the  court  of  the 
Grand-duke  Ferdinand  II  at  Florence  about  1644,  Thomas  Bartho- 
linus  gives  a  like  account  with  reference  to  the  contemporary  court 
of  King  Christian  IV  of  Denmark,  and  Poggendorff  and  Antinori 
relate  that  the  Accademia  d.  Cimento,  inspired  by  Paolo  del  Buono, 
made  trial  of  artificial  incubation  between  1651  and  1667. 

But  the  most  famous  of  all  the  attempts  to  make  artificial  as  suc- 
cessful as  natural  incubation,  were  those  of  Reaumur,  whose  book 
De  I' art  defaire  eclore  les  poulets  of  1749  achieved  a  wide  renown.  He 
devotes  many  chapters  to  a  detailed  description  of  incubators  of  very 

198  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  11 

various  kinds :  but  he  nowhere  gives  any  indication  of  his  percentage 
hatch.  It  was  probably  low.  He  speaks  also  of  the  ^^funestes  effets'^ 
of  the  vapours  of  the  dung  on  the  developing  embryos,  without,  how- 
ever, furnishing  any  foundation  for  an  exact  teratology.  In  the  second 
volume  he  describes  those  experiments  on  the  preservation  of  eggs 
by  varnishing  them,  which  caught  the  imagination  of  Maupertuis 
and  were  held  up  to  an  immortal  but  by  no  means  deserved  ridicule 
by  Voltaire  in  his  Akakia.  For  the  details  of  this  amusing  but 
irrelevant  issue  see  Miall  and  Lytton  Strachey. 

After  Reaumur,  there  were  numerous  continuations  of  the  kind  of 
work  which  he  had  done,  in  particular  by  Thevenot,  La  Boulaye, 
Nelli,  Porta  and  Cedernhielm.  Much  the  most  interesting  of  these 
was  the  work  of  Beguelin,  who  attempted  to  incubate  eggs  with 
part  of  the  shell  removed  so  as  to  form  a  round  window.  He  was  not, 
however,  successful  in  the  carrying  out  of  this  very  modern  idea. 
Probably  the  most  peculiar  investigation  made  in  this  field  at  this 
time  was  that  of  Achard,  who  is  mentioned  in  a  passage  of  Bonnet's. 
"Reaumur  did  not  suspect  in  1749",  says  Bonnet,  "that  someday 
one  would  try  to  substitute  the  action  of  the  electric  fluid  for  his 
borrowed  heat.  This  beautiful  invention  was  reserved  for  M.  Achard 
of  the  Prussian  Academy  who  excels  as  an  experimentalist.  He  has 
not  so  far  succeeded  in  actually  hatching  a  chick  by  means  of  so  new 
a  process,  but  he  has  had  one  develop  up  to  the  eighth  day,  when 
an  unfortunate  accident  deranged  his  electrical  apparatus."  Bonnet 
goes  on  to  say  that  this  substitution  of  electricity  for  heat  gives  him 
hope  that  by  electrical  means  an  artificial  fertilisation  will  one  day 
become  possible. 

The  references  to  these  experiments  and  to  those  of  many  minor 
investigators  will  be  found  in  Haller.  By  the  beginning  of  the  nine- 
teenth century  a  great  mass  of  literature  had  developed  on  the 
subject,  and  it  had  become  possible  to  hatch  out  eggs  more  or  less 
successfully  from  furnaces,  though  the  losses  were  still  great.  Early 
in  the  nineteenth  century  Bonnemain  and  Jouard  referred  to  the 
large  number  of  monsters  produced,  and  in  1809  Paris  wrote, 
"During  the  period  that  I  was  at  College,  the  late  Sir  Busick  Har- 
wood,  the  ingenious  Professor  of  Anatomy  in  the  University  of 
Cambridge,  frequently  attempted  to  develope  eggs  by  the  heat  of 
his  hotbed,  but  he  only  raised  monsters,  a  result  which  he  attributed 
to  the  unsteady  application  of  the  heat". 



This  is  the  most  convenient  place  to  mention  theological  embryo- 
logy once  again.  Its  place  in  the  eighteenth  century  was  small,  and 
in  the  nineteenth,  with  the  recognition  that  whatever  the  soul  is,  it 
is  not  a  phenomenon,  it  altogether  disappeared  from  serious  general 
discussion.  F.  E.  Cangiamilla's  Embryologia  Sacra,  however,  ran  through 
several  editions  between  1700  and  1775.  Cangiamilla  {Panorm. 
Eccl.  Can.  Theol.  et  in  toto  Sicil.  regno  contra  haereticam  pravitatem 
Inquisitore  provinciali)  deals  very  frilly  with  the  time  of  animation, 
quoting  a  host  of  writers  such  as  St  Gelasius,  St  Anselm,  Hugh  of 
St  Victor  and  Pico  della  Mirandola.  His  mind  retains  a  quite 
mediaeval  conformation,  as  the  following  curious  passage  illustrates : 
'^  Quot  non  foetus  abortivos  ex  ignorantia  obstetricum  et  matrum  excipit 
lafrina,  quorum  anima,  si  Baptismate  non  fraudaretur,  Deum  in  aeternam 
videret,  esset  decentius  tumulandum! "  His  instructions  for  the  baptism 
of  monsters  are  also  very  odd.  But  theological  embryology  probably 
reached  its  climax  in  the  report  of  the  Doctors  of  Divinity  at  the 
Sorbonne  on  March  30,  1733,  in  which  intra-uterine  baptism  by 
means  of  a  syringe  was  solemnly  recommended.  This  is  included 
in  Deventer's  book,  and  has  been  referred  to  by  Sterne  and  Spencer. 
For  other  aspects  of  these  tracts  of  thought  see  Nicholls  and  his 
anonymous  antagonist.  But  Cangiamilla  and  his  colleagues — Gerike, 
Kaltschmied,  etc. — are  only  of  decorative  importance  to  our  present 
theme,  and  for  fuller  information  regarding  them,  reference  must  be 
made  to  the  treatise  of  Witovski.  It  is  interesting  to  note  that  as 
late  as  1913,  182  days  was  fixed  as  "perfection-time",  whatever  that 
may  be,  by  Moriani. 

3*12.    Ovism  and  Animalculism 

We  must  now  return  to  the  beginning  of  the  century  in  order  to 
pick  up  the  thread  of  the  main  trend  of  thought.  By  1720  the  theory 
of  preformation  was  thoroughly  established,  not  only  on  the  erroneous 
grounds  put  forward  by  Malpighi  and  Swammerdam,  but  on  the 
experiments  of  Andry,  Hartsoeker,  Dalenpatius  and  Gautier,  who 
all  asserted  that  they  had  seen  exceedingly  minute  forms  of  men, 
with  arms,  heads,  and  legs  complete,  inside  the  spermatozoa  under 
the  microscope.  Gautier  went  so  far  as  to  say  that  he  had  seen  a 
microscopic  horse  in  the  semen  of  a  horse  (he  gave  a  plate  of  it) 
and  a  similar  animalcule  with  very  large  ears  in  the  semen  of  a 
donkey;  finally,  he  described  minute  cocks  in  the  semen  of  a  cock. 

200  EMBRYOLOGY   IN  THE   SEVENTEENTH       [pt.  ii 

Haller  remarks  gently  that  he  has  searched  for  these  phenomena  in 
vain.  Vallisneri  asserted  the  same  kind  of  thing  about  the  mammahan 
ovum,  though  he  admitted  that,  in  spite  of  long  searching,  he  had 
never  seen  one.  Besides  the  main  distinction  between  prefer mationists 
and  epigenesists,  then,  there  arose  a  division  among  the  former 
group,  so  that  the  ovists  regarded  all  embryos  as  being  produced 
from  smaller  embryos  in  the  unfertilised  eggs,  while 
the  animalculists  regarded  all  embryos  as  being 
produced  from  the  smaller  embryos  provided  by 
the  male  in  his  spermatozoa.  The  animalculists 
thus  afforded  a  singular  example  of  a  return  to 
the  ancient  theory  mentioned  by  Aeschylus  in  the 
Oresteia  (see  p.  65).  Their  most  conspicuous  ex- 
ample was  Nicholas  Andry,  who  pictured  each 
c^gg  as  being  arranged  like  the  Cavorite  sphere  in 
which  H.  G.  Wells'  explorers  made  their  way  to  the 
moon,  i.e.  with  one  trap-door.  The  spermatozoa, 
like  so  many  minute  men,  all  tried  to  occupy  an 
egg,  but  as  there  were  far  fewer  eggs  than  sperma- 
tozoa, there  were,  when  all  was  over,  only  a  few 
happy  animalcules  who  had  been  lucky  enough 
to  find  an  empty  egg,  climb  in,  and  lock  the  door 
behind  them. 

The  whole  controversy  was  intimately  bound 
up  with  the  question  of  spontaneous  generation, 
for,  whatever  the  case  might  be  in  the  higher 
animals,  if  it  were  true  that  the  lower  ones  could  arise  de  novo 
out  of  slime,  mud,  or  meat  infusion,  for  instance,  then  their  parts 
at  least  must  have  been  made  by  epigenesis,  and  not  in  any  other 
way,  for  it  could  hardly  be  held  that  a  homogeneous  infusion  had 
any  structure  of  that  kind.  And  if  epigenesis  could  occur  in  the  lower 
animals,  then  the  thin  end  of  the  wedge  had  been  driven  in,  and  it 
might  occur  among  the  higher  ones  as  well.  It  was  in  this  way  that 
the  spontaneous  generation  controversy  came  to  have  a  peculiar 
importance  for  embryology  in  the  eighteenth  century.  Driesch  has 
essayed  to  make  the  generalisation  that  all  the  supporters  of  epigenesis 
were  vitalistic  in  their  tendencies,  while  those  who  adhered  to  the 
preformation  theory  were  not.  But  there  are  too  many  exceptions 
to  this  rule  to  make  it  of  any  use.    In  so  far  as  there  is  truth  in  it. 

Fig.  1 1 .  Hartsoeker's 
drawing  of  a  human 


it  doubtless  arose  from  the  fact  that,  in  epigenesis,  a  continual  pro- 
duction of  new  organs  and  new  relationships  between  organs  already 
formed  would  seem  to  require  an  immanent  formative  force  of  some 
kind,  such  as  the  vis  essentialis  of  Wolff;  while,  on  the  preformation 
hypothesis,  where  embryogeny  was  little  more  than  a  swelling  up 
of  parts  already  there,  it  could  be  explained  as  simply  as  nutrition. 
The  failure  of  the  "short-cut"  mechanical  philosophers  such  as 
Gassendi  and  Descartes  thus  led  to  preformationism  just  as  much  as 
to  epigenesis.  A  remark  of  Cheyne's  throws  much  light  on  this 
question,  for  in  17 15  he  wrote,  unconsciously  following  Gassendi's 
line  of  thought,  "If  animals  and  vegetables  cannot  be  produced 
from  matter  and  motion  (and  I  have  clearly  proved  that  they  can- 
not), they  must  of  necessity  have  existed  from  all  eternity".  Pre- 
formationism was  thus  the  only  resource  if  the  universal  jurisdiction 
of  the  mechanical  theory  of  the  world  was  to  be  retained.  Stahl  and, 
later,  Wolff,  saw  no  point  in  retaining  it,  and  carefully  joined 
together  what  Descartes  had,  with  equal  care,  put  asunder. 

The  original  discoveries  of  de  Graaf  and  Stensen  were  extended 
by  Tauvry  in  1690  to  the  tortoise,  and  by  Lorenzini  in  1678  to  the 
Torpedo',  so  that  the  eighteenth  century  began  with  an  excellent 
basis  for  ovistic  preformationism.  The  greatest  names  associated  with 
this  school  were  Swammerdam,  Malpighi,  Bonnet,  v.  Haller,  Winslow, 
Vallisneri,  Ruysch  and  Spallanzani.  But  there  were  many  others, 
some  of  whom  did  valuable  work,  such  as  Bianchi,  Sterre,  Teichmeyer, 
Weygand,  Perrault,  Vercelloni,  Vidussi,  Bussiere,  Fizes  and  Cosch- 
witz.  The  treatises  of  Imbert  and  Plonquet  were  written  from  this 
point  of  view,  as  was  the  bright  little  dialogue  of  de  Houpeville. 
J.  B.  du  Hamel  asserted  that  he  could  see  the  chick  embryo  in  the 
Ggg  before  fertilisation,  and  Jacobaeus  made  a  like  affirmation  in  the 
case  of  the  frog. 

On  the  other  side,  that  of  animalculistic  preformationism,  the 
contestants  were  fewer.  Their  greatest  names  were  Leeuwenhoek, 
Hartsoeker,  Leibnitz  and  the  cardinal  de  Pohgnac.  In  England 
the  physicians  Keil  and  Cheque  supported  this  position,  in  France 
Geofroi  and  the  obstetrician  la  Motte,  in  Germany  Withof  and 
Ludwig,  and  in  Belgium  Lieutaud.  De  Superville  wrote  in  favour 
of  it  in  the  Philosophical  Transactions  of  the  Royal  Society,  and  an  anony- 
mous Swedish  work  of  some  fame  supported  it.  To  the  argument 
of  Vallisneri  that  the  existence  of  so  many  animalcules  must  be  an 

202  EMBRYOLOGY   IN    THE   SEVENTEENTH       [pt.  ii 

illusion,  since  Nature  could  hardly  be  so  prodigal,  the  animalculists 
retorted  by  instancing  such  observations  as  that  of  Baster,  who  had 
taken  the  trouble  to  count  the  eggs  of  a  crab  and  had  found  that 
they  amounted  to  12,444.  James  Cooke  later  elaborated  a  theory 
of  a  world  of  the  unborn  to  which  the  spermatozoa  could  retire 
between  each  attempt  to  find  a  uterus  in  which  they  could  develop — 
this  avoided  Vallisneri's  argument.  "All  those  other  attending 
Animalcula,  except  that  single  one  that  is  then  conceived,  evaporate 
away,  and  return  back  into  the  Atmosphere  again,  whence  it  is  very 
likely  they  immediately  proceeded;  into  the  open  Air,  I  say,  the 
common  Receptacle  of  all  such  disengaged  minute  sublunary  bodies; 
and  do  there  circulate  about  with  other  Semina,  where,  perhaps, 
they  do  not  absolutely  die,  but  live  a  latent  life,  in  an  insensible  or 
dormant  state,  like  Swallows  in  Winter,  lying  quite  still  like  a  stopped 
Watch  when  let  down,  till  they  are  received  afresh  into  some  other 
Male  body  of  the  proper  kind,  to  be  again  set  on  Motion,  and  ejected 
again  in  Coition  as  before,  to  run  a  fresh  chance  for  a  lucky  Con- 
ception ;  for  it  is  very  hard  to  conceive  that  Nature  is  so  idly  luxurious 
of  Seeds  thus  only  to  destroy  them,  and  to  make  Myriads  of  them 
subservient  to  but  a  single  one."  But  Cooke's  attractive  hypothesis, 
published  in  1762,  came  too  late,  as  Punnett  says,  to  save  the 

On  the  experimental  side.  Garden  and  Bourguet  came  forward 
with  descriptions  of  little  men  inside  the  animalcules,  thus  confirming 
the  work  of  Gautier  and  Hartsoeker.  It  is  fair  to  add,  however,  that 
Garden  held  quite  enlightened  views  of  the  mutual  necessity  of  egg 
and  spermatozoon.  La  Motte  maintained  that  the  egg  (which  he 
identified  with  the  Graafian  follicle)  was  too  big  to  go  down  the 
Fallopian  tube,  and  Sbaragli,  another  writer  on  the  animalculist 
side,  agreed  with  him. 

Leeuwenhoek,  it  must  be  admitted,  indulged  in  assertions  no  less 
fantastic  than  those  of  his  followers.  He  said  there  were  spermatic 
animalcules  of  both  sexes,  as  one  could  see  by  a  slight  difference  near 
their  tails,  that  they  copulated,  that  the  females  became  pregnant 
and  gave  birth  to  little  animalcules,  that  young  and  feeble  ones  could 
be  seen,  that  they  shed  their  skins,  and,  finally,  that  some  had  been 
observed  with  two  heads.  Haller,  who  made  good  use,  on  the  whole, 
of  his  strong  vein  of  scepticism,  characterised  all  these  remarks  as 
"only  conjectures".    (See  Fig.  12.) 

SECT.  3] 



As  for  the  supporters  of  epigenesis,  they  were  few,  but  they 
included  Descartes,  de  Maupertuis,  Antoine  Maitre-Jan  and  John 
Turberville  Needham.  Von  Haller  affords  some  evidence  against  the 
identification  of  epigenesis  with  vitaHsm  and  preformation  with 
mechanism,  for  he  says,  "Various  authors  have  taught  that  the  parts 
of  the  human  body  are  formed  by  a  mechanism  depending  on  general 
laws  (i.e.  laws  not  simply  of  biological  jurisdiction)  or  by  the  virtue 
of  some  ferment,  or  by  rest  and  cold  making  crusts  out  of  the  different 
juices,  or  in  other  ways.  All  these  (mechanical)  systems  have  some 
resemblance  to  that  of  M.  Wolff".  Haller  also  speaks  always  of 
Wolff's  vis  essentialis  as  "blind".  Minor  writers  on  the  epigenetic  side 
were  Tauvry,  Welsh, 
Dartiguelongue,  Bou- 
ger,  Drelincurtius  and 
Mazin.  After  1 750 
C.  F.  Wolff  brought 
an  abiding  victory  to 
their  opinion. 

Some  maintained  a 
quite  independent  po- 
sition, such  as  Buffon, 
who  welded  together 
an    epigenetic    theory 

of  fertilisation  with   a     ^^S-  12.   Dalenpatius' drawings  of  human  spermatozoa. 

preformationist  theory  of  embryogeny.  Pascal  (not  the  great  Jan- 
senist)  put  forward  the  chemical  view  that  fertilisation  consisted  of 
a  combination  between  the  acid  semen  of  the  male  and  the  "lixivious  " 
semen  of  the  female,  no  doubt  because  in  chemistry  acids  were 
regarded  as  male  and  alkalies  female.  Claude  Perrault  and  Connor 
also  suggested  that  the  formation  of  the  embryo  was  a  fermentation 
set  up  in  the  egg  by  the  spermatic  animalcule.  In  this  they  were 
following  the  example  of  van  Helmont,  who  had  originally  suggested 
such  a  theory.  In  1 763  Jacobi  discovered  how  to  fertilise  fish  eggs 
with  milt;  a  practical  matter  which  had  a  good  deal  of  influence  on 
biological  theory.  Launai  alone  still  held  to  the  Aristotelian  con- 
ception of  form  and  matter. 

There  is  no  need  here  to  do  more  than  glance  at  the  spontaneous 
generation  controversy  itself,  for  it  has  always  been  well  known  in 
the  history  of  biology,  especially  in  connection  with  the  subsequent 

204  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

work  of  Pasteur.  J.  T.  Needham's  books,  New  Microscopical  Dis- 
coveries of  1745  and  Observations  upon  the  generation,  composition,  and 
decomposition  of  animal  and  vegetable  substances  of  1 750,  exercised  a  con- 
siderable influence.  They  were  written  after  the  French  fashion 
(Needham  had  been  educated  at  Douai)  very  concisely,  and  with 
some  brilliance  of  style,  and  it  is  hardly  true  to  say,  as  Radl  does,  that 
their  experimental  foundation  was  meagre.  That  it  was  inadequate 
was  proved  definitely  as  events  turned  out  by  Spallanzani.  De 
Kruif 's  account  of  the  controversy  is  false  and  misleading,  especially 
in  its  estimate  of  Needham  who  is  much  more  truly  described  in 
the  words  of  Louis  Pasteur  (see  also  Prescott). 

Needham's  case  rested  upon  the  statement  that,  if  meat  broth  was 
placed  in  a  sealed  vessel  and  heated  to  a  high  temperature  so  that 
all  life  was  destroyed  in  it,  it  would  yet  be  found  to  be  swarming 
some  days  later  with  microscopical  animals.  All  depended,  therefore, 
upon  the  sureness  with  which  the  vessel  had  been  sealed  and  the 
efficacy  of  the  heat  employed  to  kill  all  the  animalcules  initially 
present,  and,  in  the  ensuing  controversy,  Needham  lost  to  Spallanzani 
entirely  on  a  question  of  technique.  It  may  be  remarked  here,  with- 
out irrelevance,  that  the  problem  is  still  unsolved;  for  all  that  was 
proved  by  the  experiments  of  Spallanzani  was  that  animals  the  size 
of  rotifers  and  protozoa  do  not  originate  spontaneously  from  broth, 
and  all  that  was  proved  by  those  of  Pasteur  was  that  organisms  the 
size  of  bacteria  do  not  originate  de  novo  in  that  way.  The  knowledge 
which  we  have  acquired  in  recent  years  of  filter-passing  organisms, 
such  as  the  mosaic  disease  of  the  tobacco-plant,  and  phenomena  such 
as  the  bacteriophage  of  Twort  and  d'Herelle,  has  reopened  the  whole 
matter,  so  that  of  the  region  between,  for  example,  the  semi-living 
particles  of  the  bacteriophage  (lO"^^  gram)  and  the  larger  sized 
colloidal  aggregates  (io~^^  gram)  we  know  absolutely  nothing.  The 
dogmatism  with  which  the  biologists  of  the  early  twentieth  century 
asserted  the  statement  omne  vivum  ex  vivo  was  therefore,  like  most 
dogmatisms,  ill-timed. 

But  to  dwell  further  on  this  would  be  a  digression.  The  important 
point  was  that  Spallanzani's  victory  was  a  victory  not  only  for 
those  who  disbelieved  in  spontaneous  generation,  but  also  for  those 
who  believed  in  the  preformation  theory  of  embryogeny.  By 
1 786,  indeed,  that  viewpoint  was  so  orthodox  that  Senebier,  in  his 
introduction  to  an  edition  of  Spallanzani's  book  on  the  generation 


of  animals  and  plants,  could  treat  the  epigenesists  as  no  better  than 

Spallanzani's  views  on  embryology  were  largely  drawn  from  his 
study  of  the  development  of  the  frog's  egg.  Here  he  went  far  beyond 
Bosius,  but,  in  spite  of  many  careful  observations,  he  thought  he  saw 
the  embryo  already  present  in  the  unfertilised  ova.  This  led  him  to 
claim  that  amphibia  ought  to  be  numbered  among  viviparous 
animals.  His  principal  step  forward  was  his  recognition  of  the 
semen  as  the  actual  agent  in  fertilisation  on  definite  experimental 
grounds — the  narrative  of  his  artificial  insemination  of  a  bitch 
is  too  famous  to  quote;  he  said  it  gave  him  more  intellectual  satis- 
faction than  any  other  experiment  he  had  ever  done.  This  demon- 
stration finally  disposed  of  the  aura  seminalis  which  Harvey  had 
found  himself  obliged  to  adopt  on  the  grounds  of  his  dissections  on 
does.  Curiously  enough  Spallanzani  never  convinced  himself  that 
the  spermatozoa  themselves  were  the  active  agents. 

3-13.    Preformation  and  Epigenesis 

Of  all  the  preformationists  Charles  Bonnet  was  the  most  theoretical. 
He  was  an  adherent  of  that  way  of  thinking  mainly  on  the  theoretical 
ground  that  the  organs  of  the  body  were  linked  together  in  so  intimate 
a  manner  that  it  was  not  possible  to  suppose  there  could  ever  be  a 
moment  when  one  or  two  of  them  were  absent  from  the  ranks.  "One 
needs",  he  said,  "no  Morgagni,  no  Haller,  no  Albinus  to  see  that 
all  the  constituent  parts  of  the  body  are  so  directly,  so  variously,  so 
manifoldly,  intertwined  as  regards  their  functions,  that  their  relation- 
ship is  so  tight  and  so  indivisible,  that  they  must  have  originated  all 
together  at  one  and  the  same  time.  The  artery  implies  the  vein, 
their  operation  implies  the  nerves  which  in  their  turn  imply  the 
brain  and  that  by  consequence  the  heart,  and  every  single  condition 
a  whole  row  of  other  conditions."  Bonnet  compared  epigenesis  to 
crystal-growth  in  which  particles  are  added  to  the  original  mass 
independently  of  the  plan  or  scheme  of  the  whole,  i.e.  in  opposition 
to  the  growth  of  an  organism,  in  which  particles  are  added  on  only 
at  certain  places  and  certain  times  under  the  guidance  of  "forces  de 
rapport".  Przibram  has  recently  discussed  the  question  of  how  far 
such  a  comparison  is  admissible,  but,  in  Bonnet's  time  at  any  rate, 
it  became  very  famous.  Bonnet  made  reference  to  Haller's  discovery 
of  the  intimate  relationship  between  embryo  and  yolk  as  evidence 

2o6  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

for  his  theory.  The  embryo  begins,  according  to  him,  as  an  exceedingly 
fine  net  on  the  surface  of  the  yolk,  fertilisation  makes  part  of  it  beat 
and  this  becomes  the  heart,  which,  sending  blood  into  all  the  vessels, 
expands  the  net.  The  net  or  web  catches  the  food  particles  in  its 
pores,  and  Bonnet  supposed  that,  if  it  were  possible  to  abstract  all 
the  food  particles  at  one  operation  from  the  adult  animal,  it  would 
shrivel  and  shrink  up  into  the  original  invisible  web  from  which  it 

Bonnet  was  no  more  afraid  of  the  emboitement  principle  than  was 
Haller;  indeed,  he  called  it  "one  of  the  greatest  triumphs  of  rational 
over  sensual  conviction".  Many  of  his  arguments  were  reproductions 
of  Haller's,  and  he  says  in  his  preface  that  he  had  written  his  book 
some  time  before  Haller's  papers  on  the  chick  appeared,  but  then, 
finding  his  own  views  confirmed  by  the  more  experimentally  founded 
ones  of  Haller,  he  determined  to  publish  what  he  had  set  down.  Thus 
in  one  place  he  says,  "  I  shall  be  told,  no  doubt,  that  the  observations 
on  the  development  of  the  chick  in  the  tgg  and  the  doe  in  the  maternal 
uterus  make  it  appear  that  the  parts  of  an  organised  body  are  formed 
one  after  another.  In  the  chick  for  instance  it  has  been  observed  that 
during  the  early  part  of  incubation  the  heart  seems  to  be  outside 
the  animal  and  has  a  very  diflferent  form  to  what  it  will  have.  But 
the  feebleness  of  this  objection  is  easy  to  apprehend.  Some  people 
wish  to  judge  of  the  time  when  the  parts  of  an  organised  body 
begin  to  exist  by  the  time  when  they  become  visible  to  us.  They 
do  not  reflect  that  minuteness  and  transparency  alone  can  make 
these  parts  invisible  to  us  although  they  really  exist  all  the 

Bonnet  was  therefore  what  might  be  called  an  "  organicistic  pre- 
formationist",  for  his  objection  to  epigenesis  lay  in  the  fact  that  it 
apparently  did  not  allow  for  the  integration  of  the  organism  as  a 
whole.  His  mistake  was  that  he  assumed  the  capacities  of  the  adult 
organism  to  be  present  all  through  foetal  life,  whereas  the  truth  is 
that  they  grow  and  differentiate  in  exactly  the  same  way  as  the 
physical  structure  itself  does.  Bonnet's  philosophical  position,  which 
has  been  analysed  by  Whitman,  seriously  contradicts  the  generalisa- 
tion of  Driesch  that  all  the  epigenesists  were  vitalists  and  all  the  pre- 
formationists  mechanists.  For  Bonnet  an  epigenetic  and  a  mechanical 
theory  were  one  and  the  same;  he  hardly  distinguished,  as  Radl 
says,  between  Descartes  and  Harvey;  and  it  was  just  the  neo-vitalistic 


idea  of  the  organism  as  a  whole  that  he  could  not  fit  in  with  epigenesis. 
Needham  and  Wolff  were  undoubtedly  epigenesist-vitalists,  and 
Bonnet  was  undoubtedly  a  preformationist-vitalist,  but  Maupertuis 
was  equally  clearly  an  epigenesist-mechanist. 

G.  L.  Leclerc,  Comte  de  Buffon,  the  most  independent  figure  in 
the  controversy,  stood  alone  as  much  because  of  his  erroneous  experi- 
ments as  because  of  his  originality  of  mind.  As  has  so  often  been 
observed,  Buffon  was  not  really  an  experimentalist  at  all:  he  was  a 
writer,  and  preferred  other  people  to  do  his  experiments  for  him. 
The  volume  on  generation  in  his  Histoire  Naturelle  begins  with  a  very 
long  historical  account  of  the  work  that  had  been  done  in  the  previous 
centuries  on  embryology.  At  the  beginning  of  the  section  on  repro- 
duction in  general  he  said,  "The  first  and  most  simple  manner  of 
reproduction  is  to  assemble  in  one  body  an  infinite  number  of  similar 
organic  bodies  and  to  compose  the  substance  in  such  a  manner  that 
every  part  shall  contain  a  germ  or  embryo  of  the  same  species  and 
which  might  become  a  whole  of  the  same  kind  with  that  of  which 
it  constitutes  a  part".  Such  an  idea  resembles  the  ancient  atomistic 
speculations,  and  is  explicated  by  W.  Smellie,  the  obstetrician,  who 
translated  Buffon  into  English,  as  follows:  "The  intelligent  reader 
will  perceive  that  this  sentence,  though  not  very  obvious,  contains 
the  principle  upon  which  the  whole  theory  of  generation  adopted 
by  the  author  is  founded.  It  means  no  more  than  that  the  bodies 
of  animals  and  of  vegetables  are  composed  of  an  infinite  number 
of  organic  particles,  perfectly  similar,  both  in  figure  and  substance, 
to  the  whole  animal  or  plant  of  which  they  are  the  constituent  parts ". 
This  conception  explains  Buffon's  curious  attitude  to  the  preformation 
question.  An  embryo  was  preformed  in  its  germ  because  all  the  parts 
of  the  germ  were  each  a  model  of  the  animal  as  a  whole,  but  it  was 
also  formed  by  epigenesis  because,  the  sexual  organs  being  first 
formed,  all  the  rest  arose  entirely  by  a  succession  of  new  origins. 
Buffon's  "organic,  living,  particles"  bear  some  resemblance  to  the 
"biogen  molecules"  which  later  generations  were  to  discuss,  and  he 
says  that  an  exactly  similar  but  simpler  structure  is  present  in  dead 

In  his  discussion  of  former  theories  he  resolutely  rejects  the  em- 
boitement  aspect  of  preformationism,  giving  various  calculations  to 
show  its  impossibility  and  maintaining  that  "every  hypothesis  which 
admits  an  infinite  progression  ought  to  be  rejected  not  only  as  false 

2o8        EMBRYOLOGY   IN  THE   SEVENTEENTH  [pt.  ii 

but  as  destitute  of  every  vestige  of  probability.  As  both  the  vermicular 
and  ovular  systems  suppose  such  a  progression,  they  should  be  ex- 
cluded for  ever  from  philosophy".  He  completely  destroys  the  theory 
which  the  ovists  and  animalculists  had  set  up  in  order  to  explain 
resemblance  to  parents,  namely,  that,  although  the  foetus  might 
originate  either  from  egg  or  spermatic  animalcule  originally,  it  was 
moulded  into  the  form  of  its  parents  by  the  influence  of  the  maternal 
organism  during  pregnancy.  This  field,  which  was  more  than  once 
disturbed  by  the  contestants  during  the  course  of  the  century,  re- 
ceived systematic  attention  from  time  to  time  by  medical  writers. 
There  was  a  memorable  dispute  on  this  point  between  Turner  and 
Blondel,  whose  polemics,  written  in  an  exceedingly  witty  manner, 
are  still  very  pleasant  and  amusing  to  read.  Blondel  was  the  sceptic 
and  Turner  the  defender  of  the  numerous  extraordinary  stories  which 
passed  for  evidence  on  this  subject.  It  is  interesting  to  note  that 
Turner  believed  in  the  continuity  of  foetal  and  maternal  blood-vessels. 
Krause  and  Ens  later  supported  the  opinions  of  Turner,  while  Okes, 
in  a  Cambridge  disputation,  argued  against  them. 

Buflfon's  sixth  chapter,  in  which  he  relates  the  progress  of  his  own 
experiments,  is  unfortunate,  in  that  his  main  result  was  to  discover 
spermatozoa  in  the  liquor  folliculi  of  ovaries  of  female  animals.  The 
explanation  of  how  he  came  to  make  such  an  enormous  mistake 
has  never  been  satisfactorily  given,  and  it  was  not  long  before  the 
truth  of  the  observation  was  questioned  by  Ledermuller.  It  led  him 
naturally  to  the  assertion  that  the  ovaries  of  mammalia  were  not  egg- 
producing  organs  but  animalcule-producing  organs,  and  to  the  view 
that  the  beginning  of  embryonic  development  lay  in  the  fusion  of  the 
male  with  the  female  spermatic  animalcules — a  curious  revival  of 
Epicureanism.  But  it  is  to  be  observed  that  he  does  not  mean  one 
male  animalcule  with  one  female  animalcule,  but  rather  all  with  all, 
in  a  kind  of  pangenesis.  "All  the  organic  particles",  he  says,  "which 
were  detached  from  the  head  of  the  animal  will  arrange  themselves 
in  a  similar  order  in  the  head  of  the  foetus.  Those  which  proceeded 
from  the  backbone  will  dispose  themselves  in  an  order  corresponding 
to  the  structure  and  position  of  the  vertebrae".  And  so  on  for  all 
the  organs.  The  fact  that  for  the  organs  common  to  both  sexes  a 
double  set  of  animalcules  will  thus  be  provided  does  not  give  Buffon 
any  difficulty  and  is  fully  admitted  by  him.  Accordingly  he  could 
only   agree   to    the   aphorism   omne    vivum  ex   ovo   in    the   sense   of 


Harvey,  namely,  as  referring  to  the  egg-shaped  chorion  of  vivipara, 
and  definitely  not  in  the  sense  of  de  Graaf  and  Stensen,  namely,  in 
the  modern  sense.  "Eggs",  he  says,  "instead  of  being  common  to 
all  females,  are  only  instruments  employed  by  Nature  for  supplying 
the  place  of  uteri  in  those  animals  which  are  deprived  of  this  organ. 
Instead  of  being  active  and  essential  to  the  first  impregnation,  eggs 
are  only  passive  and  accidental  parts,  destined  for  the  nourishment 
of  the  foetus  already  formed  in  a  particular  part  of  this  matrix 
by  the  mixture  of  the  male  and  female  semen."  Biology  at  this  period 
was  still  labouring  under  the  disadvantage  of  being  without  the  cell- 
theory,  and  therefore  unable  to  distinguish  between  an  egg  and  an 

In  spite  of  his  leanings  towards  epigenesis,  Buffon  repeats  precisely 
the  error  of  Malpighi.  "I  formerly  detected",  he  says,  "the  errors 
of  those  who  maintained  that  the  heart  or  the  blood  was  first 
formed.  The  whole  is  formed  at  the  same  time.  We  learn  from  actual 
observation  that  the  chicken  exists  in  the  egg  before  incubation.  The 
head,  the  backbone,  and  even  the  appendages  which  form  the 
placenta  are  all  distinguishable.  I  have  opened  a  great  number  of 
eggs  both  before  and  after  incubation  and  I  am  convinced  from  the 
evidence  of  my  own  eyes  that  the  whole  chicken  exists  in  the  middle 
of  the  cicatrice  the  moment  the  egg  issues  from  the  body  of  the  hen. 
The  heat  communicated  to  it  by  incubation  expands  the  parts  only. 
But  we  have  never  been  able  to  determine  with  certainty  what  parts 
of  the  foetus  are  first  fixed,  at  the  moment  of  its  formation."  The 
experiment  of  taking  a  look  at  the  cicatrices  of  eggs  on  their  way 
down  the  parental  oviduct  is  so  obvious  that  Buffon  must  have  thought 
of  it,  and  it  would  be  really  interesting  to  know  what  factor  in  the 
intellectual  climate  it  was  that  made  him  regard  such  an  observation 
as  not  worth  attempting.  His  observations  on  the  embryo  itself  were 
good  and,  in  some  ways,  new;  thus  he  noticed  that  the  blood  first 
appears  on  the  "placenta"  or  blastoderm,  and  for  the  first  few  days 
seems  hardly  to  enter  the  body  of  the  embryo.  He  gave  an  extremely 
good  account  of  the  whole  developmental  process  in  the  chick  and 
in  man,  and  his  opinions  on  the  use  of  the  amniotic  liquid  and  the 
functions  of  the  umbilical  cord  were  very  advanced. 

J.  T.  Needham,  however,  spoke  very  clearly  in  favour  of  epi- 
genesis, though  he  himself  did  no  embryological  experiments.  His 
Idee  sommaire  of  1776,  written  against  Voltaire,  who  had  called  him 

N  E  I  14 


a  Jesuit  and  who  had  drawn  materialistic  inferences  from  his  writings, 
contained  the  following  passage:  "The  numerous  absurdities  which 
exist  in  the  opinion  ofpre-existent  germs  together  with  the  impossibility 
of  explaining  on  that  ground  the  birth  of  monsters  and  hybrids,  made 
me  embrace  the  ancient  system  of  epigenesis,  which  is  that  of  Aristotle, 
Hippocrates,  and  all  the  ancient  philosophers,  as  well  as  of  Bacon 
and  a  great  number  of  savants  among  the  neoteriques.  My  observa- 
tions also  led  me  directly  to  the  same  result".  Needham's  embryology 
is  mostly  contained  in  his  Observations  nouvelles  sur  la  Generation  of 
1750.  He  was  explicitly  a  Leibnitzian  and  postulated  a  vegetative 
force  in  every  monad. 

Needham  was  not  the  only  thoroughgoing  epigenesist  of  this 
period.  Maupertuis,  whose  Venus  Physique  was  published  anony- 
mously in  1746,  came  out  very  clearly  on  the  side  of  epigenesis. 
"I  know  too  well",  he  said,  "the  faults  of  all  the  systems  which  I 
have  been  describing,  to  adopt  any  one  of  them,  and  I  find  too 
much  obscurity  in  the  whole  matter  to  wish  to  form  one  of  my  own. 
I  have  but  a  few  vague  thoughts  which  I  propose  rather  as  thoughts 
to  be  examined  than  as  opinions  to  be  received,  and  I  shall  neither 
be  surprised  nor  think  myself  aggrieved  if  they  are  rejected.  It  seems 
to  me  that  both  the  system  of  eggs  and  that  of  spermatic  animal- 
cules are  incompatible  with  the  manner  in  which  Harvey  actually 
saw  the  embryo  to  be  formed.  And  one  or  the  other  of  these  systems 
seems  to  me  still  more  surely  destroyed  by  the  resemblance  of  the 
child,  now  to  the  father  and  now  to  the  mother,  and  by  hybrid 
animals  which  are  born  from  two  different  species. ...  In  this  ob- 
scurity in  which  we  find  ourselves  on  the  manner  in  which  the  foetus 
is  formed  from  the  mixture  of  two  liquors,  we  find  certain  facts  which 
are  perhaps  a  better  analogy  than  what  happens  in  the  brain.  When 
one  mixes  silver  and  spirits  of  nitre  with  mercury  and  water,  the 
particles  of  these  substances  come  together  themselves  to  form  a 
vegetation  so  like  a  tree  that  it  has  been  impossible  to  refuse  it  the 
name."  This  was  the  Arbor  Dianae,  which  played  a  great  part  in 
these  embryological  controversies  of  the  eighteenth  century.  It  has 
a  great  interest  for  us,  for  it  was  perhaps  the  first  occasion  on  which 
a  non-living  phenomenon  had  been  appealed  to  as  an  illustration 
of  what  went  on  in  the  living  body.  It  is  true  that  Descartes  long 
before  had  said  that  the  movements  of  the  living  body  were  carried 
out  by  mechanisms  like  clocks  or  watches,  and  that  they  resembled 


the  statues  in  certain  gardens  which  could  be  made  to  perform  un- 
expected functions  by  the  pressure  of  a  manipulator's  foot  on  a 
pedal,  but  these  instances  were  all  artificially  constructed  mechanical 
devices,  whereas  the  Arbor  Dianae  was  a  natural  phenomenon  quite 
unexplained  by  the  chemists  of  the  time,  and  the  lineal  forerunner 
of  Lillie's  artificial  nerve,  and  Rhumbler's  drop  of  chloroform.  We 
know  now  that  its  formation  is  a  simpler  process  than  anything 
which  occurs  in  the  developing  embryo,  but  the  course  of  research  has 
made  it  undeniably  clear  that  the  same  forces  which  operate  in  the 
formation  of  the  Arbor  Dianae  are  at  work  also  in  the  developing 
embryo.  To  this  extent  Maupertuis  is  abundantly  justified,  and 
Driesch's  comments  on  him  are  not  in  agreement  with  the  facts. 

"Doubtless  many  other  productions  of  a  like  kind  will  be  found", 
Maupertuis  goes  on,  "if  they  are  looked  for  or  perhaps  if  they  are 
looked  for  less.  And  although  they  seem  to  be  less  organised  than 
the  body  of  most  animals,  may  they  not  depend  on  the  same  mechanics 
and  on  similar  laws?  Will  the  ordinary  laws  of  motion  suffice,  or 
must  we  have  recourse  to  new  forces?  These  forces,  incomprehensible 
as  they  are,  appear  to  have  penetrated  even  into  the  Academy  of 
Sciences  at  Paris,  that  institution  where  so  many  opinions  are  weighed 
and  so  few  admitted."  Maupertuis  goes  on  to  speak  of  the  contem- 
porary deliberations  on  the  subject  of  attraction.  "Ghymistry",  he 
says,  "has  felt  the  necessity  of  adopting  this  conception  and  attractive 
force  is  nowadays  admitted  by  the  most  famous  chymists  who  have 
carried  the  use  of  it  far  beyond  the  point  which  the  astronomers 
had  reached.  If  this  force  exists  in  nature,  why  should  it  not  take 
part  in  the  formation  of  animals?"  Maupertuis  was  thus  an  epi- 
genesist  and  a  mechanist  at  the  same  time.  His  opinions  have  an 
extremely  modern  ring,  and  his  only  retrograde  step  was  in  suggesting 
that  the  spermatic  animals  had  nothing  else  to  do  except  to  mix  the 
two  seeds  by  swimming  about  in  them.  But  that  legacy  of  ovism 
was  common  all  through  the  eighteenth  century,  and  thirty  years 
later  Alexander  Hamilton  could  say,  "From  the  discovery  of  Animal- 
cula  in  semine  masculino  by  Leeuwenhock's  Glasses,  a  new  Theory  was 
adopted  which  is  not  yet  entirely  exploded". 

But  the  real  middle  point  and  fulcrum  of  the  whole  period  lay  in 
the  controversy  between  von  Haller  and  Caspar  Friedrich  Wolflf,  the 
former  at  Gottingen  and  the  latter  at  St  Petersburg  in  the  Academy 
of  the  Empress  Catherine.    Kirchhoflf  has  described  this  polemic. 


212  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 

Wolff's  Theoria  generationis,  which  was  a  defence  of  epigenesis  on 
theoretical  and  philosophical  grounds,  written  in  a  very  formal, 
logical,  and  unreadable  manner,  appeared  when  he  was  only  twenty- 
six  years  old,  in  1759.  Leibnitz,  as  Radl  points  out,  had  borrowed 
from  the  earlier  preformationists  the  conception  of  a  unit  increasing 
in  bulk  in  order  to  become  another  kind  of  unit;  but  Wolff,  following 
Needham,  borrowed  from  Leibnitz  the  idea  of  a  monad  developing 
into  an  organism  by  means  of  its  own  inherent  force,  and  to  this  he 
joined  the  Stahlian  notion  of  a  generative  supra-physical  force  in 
nature.  On  the  practical  side,  Wolff's  work  was  indeed  of  the  highest 
importance.  If  the  embryo  pre-exists,  he  argued,  if  all  the  organs 
are  actually  present  at  the  very  earliest  stages  and  only  invisible  to 
us  even  with  the  highest  powers  of  our  microscopes,  then  we  ought 
to  see  them  fully  formed,  as  soon  as  we  see  them  at  all.  In  other 
words,  at  the  moment  at  which  any  given  organ  comes  into  view,  it 
ought  to  have  the  form  and  shape,  though  not  the  size,  of  the  same 
organ  when  fully  completed  in  the  embryo  at  birth.  On  the  other 
hand,  if  this  is  not  the  way  in  which  development  goes  on,  then  one 
ought  to  be  able  to  see  with  the  microscope  one  shape  changing  into 
another  shape,  and,  in  fact,  a  series  of  appearances,  each  one  different 
from  that  which  had  immediately  preceded  it,  or,  in  other  words, 
a  series  of  advancing  adaptations  of  the  various  parts  of  the  primitive 
embryonic  mass.  WoliT  chose  as  his  first  test  case  the  blood-vessels 
of  the  blastoderm  in  the  chick,  for  he  saw  that  at  one  moment  this 
apparatus  was  in  existence,  while  the  moment  before  it  had  not  been. 
His  microscopical  researches  led  him  to  the  conclusion  that  the  homo- 
geneous surface  of  the  blastoderm  partially  liquefies  and  transforms 
itself  at  these  points  into  a  mass  of  islands  of  solid  matter,  separated  by 
empty  spaces  filled  with  a  colourless  liquid  but  afterwards  with  a  red 
liquid,  the  blood.  Finally,  these  spaces  are  covered  with  membranes 
and  become  vessels.  Consequently  it  was  obvious  that  the  vessels  had 
not  been  previously  formed,  but  had  arisen  by  epigenesis. 

Haller  replied  to  this  new  experimental  foundation  for  epigenesis 
without  delay,  for  he  was  working  on  the  development  of  the  chick 
at  the  same  time,  and  held  closely  to  the  opposite  theory.  We  have 
already  seen  what  his  one  and  only  argument  against  Wolff  was.  He 
used  it  time  after  time  in  all  its  possible  variations,  maintaining  stoutly 
that  the  chick  embryo  was  so  fluid  in  the  early  stages  that  Wolff  had 
no  right  to  deny  the  presence  of  a  given  structure  simply  because 


he  could  not  see  it.  Haller's  explanation  of  Wolff's  results  was  that 
the  blood-vessels  had  been  there  all  the  time  but  that  they  had  not 
become  visible  until  the  moment  at  which  Wolff  saw  the  islands 
forming.  "After  I  had  written  the  above",  said  Haller,  "M.  Wolff 
made  new  objections  against  the  demonstration.  Instructed  by  new 
researches,  he  denies  absolutely  that  the  yolk-membranes,  which  he 
makes  two  in  number,  exist  before  incubation.  He  pretends  that  they 
are  new  and  that  they  are  born  at  the  beginning  of  incubation,  and 
consequently  that  the  continuity  of  their  vessels  with  the  embryo 
does  not  in  the  least  prove  that  in  the  body  of  the  mother  the  yolk 
received  vessels  from  the  foetus.  I  have  compared  the  observations 
of  this  great  man  with  my  own  and  I  have  found  that  the  yolk 
never  has  more  than  one  pulpy  and  soft  membrane,  part  of  which 
is  what  I  have  called  the  umbilical  area,  and  that  the  fine  exterior 
membrane  does  not  belong  to  the  yolk  but  to  the  inner  part  of  the 
umbilical  membrane. ...  I  do  not  believe  that  any  new  vessels  arise 
at  all,  but  that  the  blood  which  enters  them  makes  them  more 
obvious  because  of  the  colour  which  it  gives  them,  and  so  by  the 
augmentation  of  their  volume,  they  become  longer." 

Wolff  replied  by  another  extensive  piece  of  work,  which  he  called 
De  Formatione  Intestinorum,  and  which  appeared  in  one  of  the  publica- 
tions of  the  Russian  Academy  for  1768.  It  ruined  preformationism. 
In  it  he  demonstrated  that  the  intestine  is  formed  in  the  chick  by 
the  folding  back  of  a  sheet  of  tissue  which  is  detached  from  the  ventral 
surface  of  the  embryo,  and  that  the  folds  produce  a  gutter  which  in 
course  of  time  transforms  itself  into  a  closed  tube.  The  intestine, 
therefore,  could  not  possibly  be  said  to  be  preformed,  and  from  this  as 
starting-point,  Wolff  went  on  to  propose  an  epigenetic  theory  which 
applied  the  same  process  to  all  organs.  It  is  interesting  to  note  that 
the  facts  brought  forward  by  Wolff  have  never  been  contradicted,  but 
have  been  used  as  a  foundation  to  which  numberless  morphological 
embryologists  have  added  facts  discovered  by  themselves.  It  is 
noteworthy  that,  although  Wolff's  second  general  principle,  that  of 
increasing  solidification  during  embryonic  development,  led  to  no 
immediate  results,  it  has  been  abundantiy  confirmed  since  then  (see 
Fig.  221).  His  observations  on  the  derivation  of  the  parts  of  the  early 
embryo  from  "leaf-like"  layers  were  even  more  important,  and  acteA 
as  a  very  potent  influence  in  the  work  of  Pander  and  von  Baer. 

It   happened,  however,  that  Haller  had  much   the  greater  in- 

214  EMBRYOLOGY   IN   THE   SEVENTEENTH        [pt.  ii 

fluence  in  the  biological  world  at  the  time,  so  that  Wolff's  conceptions 
did  not  immediately  yield  fruit  in  any  general  advance.  Looking 
back  over  the  second  half  of  the  seventeenth  and  the  first  two-thirds 
of  the  eighteenth  century,  it  is  remarkable  how  little  theoretical 
progress  was  made  in  view  of  the  abundance  of  new  facts  which  were 
discovered.  Punnett,  in  an  interesting  paper,  has  vividly  brought  this 
out.  "The  controversy  between  the  Ovists  and  Animalculists  had 
lasted  just  a  century",  he  says,  "and  it  is  not  uninteresting  to  reflect 
that  the  general  attitude  of  science  towards  the  problem  of  generation 
was  in  1775  niuch  what  it  had  been  in  1675.  When  the  period  opened, 
almost  all  students  of  biology  and  medicine  were  Preformationists 
and  Ovists;  at  its  close  they  were  for  the  most  part  Ovists  and  Pre- 
formationists." Ovism  sprang  in  the  first  instance  from  de  Graaf's 
discovery  of  the  mammalian  egg,  which  gave  a  new  and  precise 
meaning  to  Harvey's  aphorism.  Preformationism,  already  old  as  a 
theory,  acquired  an  apparent  factual  basis  in  the  work  of  Malpighi 
and  Swammerdam,  and  allied  itself  naturally  with  ovism.  With 
Leeuwenhoek  and  his  spermatozoa,  animalculism  came  upon  the 
field.  The  main  outlines  of  the  battle  which  went  on  between  the 
two  viewpoints  have  already  been  drawn,  but  it  is  worth  remembering 
that  there  were  independent  minds  who  were  impressed  by  the  obvious 
facts  of  heredity  and  found  it  difficult  to  call  one  sex  essential  rather 
than  the  other.  Among  these  Needham  and  Maupertuis  might  be 
counted,  and  among  the  lesser  men,  James  Handley  with  his  Me- 
chanical Essays  on  the  Animal  Oeconomy  of  1730  ought  to  receive  a 
mention.  Though  fond  of  theological  arguments  he  upheld  the 
common-sense  attitude  against  ovists  and  animalculists  alike — "We 
dissent  in  some  things",  he  said,  "both  from  Leeuwenhoeck  and 
Harvey. .  .  .  Both  the  semen  and  ova  (notwithstanding  all  that  can 
be  said)  we  believe  to  be  a  causa  sine  qua  non  in  every  Generation". 
But  what  finally  killed  animalculism  was  the  discovery  in  so  many 
places  of  small  motile  living  beings,  flagellates,  protozoa,  large 
vibrios.  It  was  difficult  to  maintain  in  the  face  of  this  new  evidence 
that  the  spermatozoa  were  essential  elements  in  generation,  though 
the  seminal  fluid  itself  might  very  well  be,  as  of  course  was  Spallan- 
zani's  opinion.  The  preformation  theory  was  what  was  holding  up 
further  progress,  and  when  Wolff's  arguments  prevailed  in  the  very 
last  years  of  the  eighteenth  century,  the  way  was  open  for  the 
recognition  of  the  true  value  of  the  spermatozoa. 


The  otherwise  unknown  physician  d'Aumont,  who  wrote  the 
article  on  "Generation"  in  Diderot's  famous  Encyclopaedia,  brought 
this  out  in  an  interesting  way,  for  himself  an  ovist,  he  summarised 
the  arguments,  which,  in  1757,  were  destroying  the  animalculist 
position,  and  reducing  rapidly  the  number  of  its  adherents. 

1.  Nature  would  never  be  so  prolific  as  to  produce  such  millions 
of  spermatic  animalcules,  each  one  with  its  soul,  unnecessarily. 

2.  The  spermatic  animalcules  of  all  animals  are  the  same  size,  no 
matter  how  large  the  animal  is:  how,  therefore,  can  they  be 
involved  in  its  generation? 

3.  They  are  never  found  in  the  uterus  after  coitus,  but  only  in 
the  sperm  (?). 

4.  How  do  they  reproduce  their  kind? 

5.  What  evidence  is  there  that  they  are  any  different  from  the 
animalcules  (of  similar  shape,  etc.)  which  are  to  be  found  in 
hay  infusion,  scrapings  from  the  teeth,  etc.  ?  Nobody  supposes 
that  these  have  any  relation  to  reproduction. 

3-14.    The  Close  of  the  Eighteenth  Century 

The  last  forty  years  of  the  century  were  not  marked  by  any  great 
movement  in  a  fruitful  direction  for  morphological  embryology,  an 
iconographic  wave  of  some  merit  due  to  Albinus,  W.  Hunter,  Tarin, 
Senffj  Rosenmuller,  Danz  and  Soemmering  excepted ;  and  it  was  not 
until  181 2  that  J.  F.  Meckel  the  younger  translated  Wolff's  papers 
into  German.  This  was  one  of  the  principal  influences  upon  Pander 
and  von  Baer.  In  his  introduction,  Meckel  describes  how  Wolff's 
work  had  been  disregarded,  and  points  out  that  Oken,  writing  in 
1806,  had  apparently  never  even  heard  of  it.  In  the  very  early 
years  of  the  nineteenth  century  morphological  embryology  received 
a  great  impetus,  however.  One  of  the  most  interesting  figures  of 
the  new  period  was  de  Lezerec,  a  Breton,  whose  father  had  been 
in  the  Russian  naval  service.  The  son,  as  a  Russian  naval  cadet,  no 
doubt  stimulated  by  the  writings  of  Wolff,  who  had  lived  at  St  Peters- 
burg, used  to  incubate  eggs  on  board  ship.  He  eventually  left  the 
sea,  studied  medicine  at  Jena,  and  wrote  an  excellent  dissertation 
on  the  embryology  of  the  chick  in  1 808,  which  Stieda  has  recently 
brought  to  light.  He  then  went  to  Paris,  and,  taking  a  medical 
appointment  at  Guadeloupe,  was  lost  to  science.  Very  much  more 
important  was  the  work  of  Pander  in  181 7  and  von  Baer  in  1828, 

2i6  EMBRYOLOGY   IN  THE   SEVENTEENTH       [pt.  ii 

but  it  belongs  to  the  present  period,  and  I  shall  not  treat  it  historically. 
For  data  on  von  Baer,  see  Kirste,  Addison  and  Stieda.  It  is  interesting 
to  note,  however,  that  the  recapitulation  theory,  which  was  first  clearly 
formulated  by  von  Baer,  was  already  taking  shape  in  various  minds 
during  the  closing  years  of  the  eighteenth  century.  Lewes  has  thus 
described  the  thesis  of  Goethe's  Morphologie,  written  in  1795:  "The 
more  imperfect  a  being  is  the  more  do  its  individual  parts  resemble 
each  other  and  the  more  do  these  parts  resemble  the  whole.  The  more 
perfect  a  being  is  the  more  dissimilar  are  its  parts.  In  the  former  case 
the  parts  are  more  or  less  a  repetition  of  the  whole,  in  the  latter 
case  they  are  totally  unlike  the  whole.  The  more  the  parts  resemble 
each  other  the  less  subordination  is  there  of  one  to  the  other :  and 
subordination  is  the  mark  of  high  grade  of  organisation". 

William  and  John  Hunter  belong  also  to  the  end  of  the  century. 
The  former,  in  his  book  on  the  anatomy  of  the  gravid  uterus,  proved 
finally  and  completely  the  truth  of  the  view  that  the  maternal  and 
foetal  circulations  are  distinct.  His  injections  left  no  shadow  of  doubt 
about  the  matter,  and  the  way  was  clearly  opened  up  for  the  study 
of  the  properties  of  the  capillary  endothelial  membranes  separating 
the  bloods,  a  study  which  is  still  vigorously  proceeding,  especially 
in  its  physico-chemical  aspect  (see  Section  21).  There  was  a  quarrel 
between  the  brothers  over  the  priority  of  this  demonstration.  John 
Hunter's  Essays  and  Observations  also  contain  material  important  for 
embryology.  His  drawings  of  the  chick  in  the  &gg  were  very  beautiful, 
and  are  still  in  the  archives  of  the  Royal  College  of  Surgeons.  He 
adopted  Mayow's  theory  of  the  office  of  the  air-space,  and  anticipated 
von  Baer's  theory  of  recapitulation  much  as  did  Goethe.  "If  we  were 
capable  of  following  the  progress  of  increase  of  the  number  of  parts 
of  the  most  perfect  animal  as  they  were  first  formed  in  succession, 
from  the  very  first  to  its  state  of  full  perfection,  we  should  probably 
be  able  to  compare  it  with  some  one  of  the  incomplete  animals 
themselves,  of  every  order  of  animals  in  the  creation,  being  at  no 
stage  different  from  some  of  the  inferior  orders.  Or,  in  other  words, 
if  we  were  to  take  a  series  of  animals,  from  the  more  imperfect  to 
the  perfect,  we  should  probably  find  an  imperfect  animal  corre- 
sponding with  some  stage  of  the  most  perfect."  It  is  impossible  not 
to  reflect  on  the  curious  course  which  was  taken  by  the  essence  of 
the  idea  of  recapitulation  in  the  history  of  embryology.  As  Aristotle 
first  formulated  it,  it  was  as  much  bodily  as  mental,  but  all  his  sue- 


cessors  until  the  eighteenth  century  a.d.  treated  it  as  a  psychological 
rather  than  a  physiological  or  morphological  theory,  and  lost  them- 
selves in  speculations  about  the  vegetative,  sensitive,  and  rational 
souls.  Yet  the  other  aspect  of  the  theory  was  only  asleep,  and  was 
destined  to  be  of  the  greatest  value  as  soon  as  investigators  began  to 
direct  their  attention  more  to  the  material  than  to  the  spiritual 
aspect  of  the  developing  being. 

Hunter  did  not  absolutely  reject  preformationism,  but  regarded  it 
as  holding  good  for  some  species  in  the  animal  kingdom ;  he  therefore 
attached  no  philosophical  importance  to  it. 

Although  Wolff's  work  did  not  lead  to  the  immediate  morphological 
advances  which  might  have  been  expected,  it  was  in  many  ways 
fruitful.  It  produced  J.  F.  Blumenbach's  Uber  den  Bildungstrieb  of 
1789,  a  work  which  elaborated  the  Wolffian  vis  essentialis  into 
the  nisus  formativus,  a  directing  morphogenetic  force  peculiar  to 
living  bodies.  It  is  interesting  to  note  that  Blumenbach  passed  through 
an  exactly  opposite  succession  of  opinions  to  that  of  Haller,  i.e.  he 
was  first  attracted  by  preformationism,  but,  being  convinced  by 
Wolff's  work,  abandoned  it  in  favour  of  epigenesis.  Blumenbach 
compares  his  nisus  formativus  with  the  force  of  gravity,  regarding 
them  as  exactly  similar  conceptions  and  using  them  simply  as 
definitions  of  a  force  whose  constant  effects  are  recognised  in 
everyday  experience.  Blumenbach  says  that  his  nisus  formativus 
differs  from  Wolff's  vis  essentialis  because  it  actively  does  the  shaping 
and  does  not  merely  add  suitable  material  from  time  to  time  to  a 
heap  of  material  which  is  already  engaged  in  shaping  itself.  Wolff 
was  still  alive  at  this  time,  but  he  did  not  make  any  comment  on 
Blumenbach,  though  he  might  very  well  have  said  that  Blumenbach 
had  misunderstood  him,  and  that  their  forces  were  really  alike  in 
every  particular.  Both  Blumenbach  and  Wolff  were  mentioned  by 
Kant  in  the  Critique  of  Judgement  where  he  adopted  the  epigenetic 
theory  in  his  discussion  of  embryogeny. 

A  word  must  be  said  at  this  point  about  the  opinions  of  the 
eighteenth  century  on  foetal  nutrition.  At  the  beginning  of  it,  there 
was,  as  has  been  shown,  a  welter  of  conflicting  theories;  and  though, 
later  on,  writers  on  this  subject  were  fewer,  the  progress  made  was 
no  more  rapid.  In  1802  Lobstein  was  supporting  the  view  (which 
had  been  defended  by  Boerhaave)  that  the  amniotic  liquid  nourished 
the  embryo  per  os,  although  Themel  had  shown  forty  years  before 






that  this  could  be  at  most  the  very  slightest  source  of  material,  from 
a  study  of  acephalic  monsters.  These  workers  had  obviously  learnt 
nothing  from  Herissant  and  Brady,  who  had  been  over  precisely  the 
same  ground  fifty  years  before.  On  the  other  hand.  Goods  and 
Osiander  reported  the  birth  of  embryos  without  umbilical  cords,  so 
that  the  solution  of  this  question  became,  in  the  first  year  of  the 
nineteenth  century,  balanced,  as  it  were,  between  the  relative 
credibility  of  two  kinds  of  prodigy.  Nourishment  per  os  was  defended 
by  Kessel,  Hannes  and  Grambs,  and  was  attacked  by  Vogel,  Bern- 
hard,  Glaser,  Hannhard  and  Reichard.  The  idea  lingered  on  right 
into  the  modern  period,  and  as  late  as  1 886  von  Ott,  who  was  much 
puzzled  about  placental  permeability,  decided  that  a  great  part  in 
foetal  nutrition  must  be  played  by  the  amniotic  liquid.  WeidHch, 
a  student  of  his,  fed  a  calf  on  amniotic  liquid  for  some  days,  and  as 
it  seemed  to  get  on  all  right,  he  reported  the  amniotic  liquid  to  have 
nutritive  properties.  The  appeal  to  monsters  was  still  resorted  to  at 
the  end  of  the  nineteenth  century,  for  Opitz,  in  order  to  negative  von 
Ott's  conclusions,  drew  attention  to  a  specimen  in  the  Chemnitz 
Polyklinik  in  which  the  oesophagus  of  a  well-nourished  normal  infant 
was  closed  at  the  upper  third  without  the  development  of  the  body 
having  been  in  any  way  restricted.  The  fuller  possibilities  of  bio- 
chemistry itself  have  sometimes  been  exploited  in  favour  of  the  ancient 
theory  of  nourishment />^r  os\  thus  Kottnitz  in  1889  collected  some 
data  about  the  presence  of  peptones  and  protein  in  the  human 
amniotic  liquid  with  this  object  in  view.  That  the  foetus  swallows 
the  liquid  which  surrounds  it  towards  the  end  of  gestation  in  all 
amniota,  can  hardly  be  disputed,  and  as  there  are  known  to  be 
active  proteolytic  enzymes  in  the  intestinal  tract,  no  doubt  some  of 
the  protein  which  it  contains  is  digested — but  to  maintain  that  any 
significant  part  is  played  in  foetal  nutrition  by  this  process  has 
become  steadily  more  and  more  impossible  since  1600. 

But  to  return  to  the  eighteenth  century;  all  was  not  repetition; 
occasionally  somebody  brought  forward  a  few  facts.  Thus  the  de- 
glutition of  the  amniotic  Hquid  was  discussed  by  Flemyng  in  1 755 
in  a  paper  under  the  title  "  Some  observations  proving  that  the  foetus 
is  in  part  nourished  by  the  amniotic  liquor".  "I  believe",  he  said, 
"that  very  few,  if  any  at  all,  will  maintain  now-a-days  with  Claudius 
de  la  Courvee  and  Stalpartvan-der-Wiel,  that  the  whole  of  its  nourish- 
ment is  conveyed  by  the  mouth."    But  he  himself  had  found  white 

220  EMBRYOLOGY   IN   THE   SEVENTEENTH        [pt.  ii 

hairs  in  the  meconium  of  a  calf  embryo  with  a  white  hide.  Both 
Aides  and  Swammerdam  had  found  the  same  thing,  but  Aides  did 
not  think  it  of  any  significance,  and  Swammerdam  merely  remarked 
that  the  calf  must  lick  itself  in  utero. 

More  interesting  was  W.  Watson's  "Some  accounts  of  the  foetus 
in  utero  being  differently  affected  by  the  Small  Pox".  This  was  the 
earliest  investigation  of  the  permeability  of  the  placenta  to  patho- 
logical agents.  "That  the  foetus",  said  Watson,  "does  not  always 
partake  of  the  Infection  from  its  Mother,  or  the  Mother  from  the 
Foetus,  is  the  subject  of  this  paper."  Two  of  his  cases,  he  said,  "evince 
that  the  Child  before  its  Birth,  though  closely  defended  from  the 
external  Air,  and  enveloped  by  Fluids  and  Membranes  of  its  own,  is 
not  secure  from  the  variolous  Infection,  though  its  Mother  has  had 
the  Distemper  before.  They  demonstrate  also  the  very  great  Subtility 
of  the  variolous  Effluvia".  But  other  cases  "are  the  very  reverse  of 
the  former,  where  though  from  Inoculation  the  most  minute  portion 
of  Lint  moisten'd  with  the  variolous  Matter  and  applied  to  the  slightly 
wounded  Skin,  is  generally  sufficient  to  propagate  this  Distemper; 
yet  here  we  see  the  whole  Mass  of  the  Mother's  Blood,  circulating 
during  the  Distemper  through  the  Child,  was  not  sufficient  to  pro- 
duce it. .  .  .  From  these  Histories  it  appears  that  the  Child  before  its 
Birth  ought  to  be  consider'd  as  a  separate,  distinct  Organization; 
and  that  though  wholly  nourish'd  by  the  Mother's  Fluids,  with 
regard  to  the  Small  Pox,  it  is  liable  to  be  affected  in  a  very  different 
Manner  and  at  a  very  different  Time  from  its  Mother".  Doubtless 
the  modern  explanation  of  Watson's  discordant  results  would  be  that! 
in  one  case  there  were  placental  lesions,  destroying  the  perfect  barrier 
between  the  circulations,  and  in  others  there  were  not. 

In  the  last  year  of  the  century  (but  the  seventh  of  the  Republic) 
Citizens  Leveille  &  Parmentier  contributed  an  interesting  paper  to  I 
the  Journal  de  Physique  in  which  they  observed  the  increase  in  size] 
of  the  avian  yolk  on  incubation  and  spoke  of  a  current  of  water  yolk- 
wards  (see  Fig.  225). 

3*  15.    The  Beginning  of  the  Nineteenth  Century 

At  the  beginning  of  the  new  century  a  fresh  influence  came  in! 
with  the  work  of  Lamarck,  though  it  did  not  have  such  a  great  effect 
on  his  contemporaries  as  on  later  generations.    Its  relations  with] 
biochemistry  are  so  remote  that  there  is  no  need  to  deal  in  any  detail 


with  it  here,  but  Lamarck's  opinions  on  embryology  may  perhaps 
be  given  in  the  words  of  Cuvier,  written  in  1836. 

"In  1802  he  pubUshed  his  researches  on  living  bodies,  containing 
a  physiology  peculiar  to  himself,  in  the  same  way  that  his  researches 
on  the  principal  facts  of  physics  contained  a  chemistry  of  that  char- 
acter. In  his  opinion  the  egg  contains  nothing  prepared  for  life 
before  being  fecundated,  and  the  embryo  of  the  chick  becomes 
susceptible  of  vital  motion  only  by  the  action  of  the  seminal  vapour; 
but,  if  we  admit  that  there  exists  in  the  universe  a  fluid  analogous 
to  this  vapour,  and  capable  of  acting  upon  matter  placed  in  favour- 
able circumstances,  as  in  the  case  of  the  embryon,  which  it  organises 
and  fits  for  the  enjoyment  of  life,  we  will  then  be  able  to  form  an 
idea  of  spontaneous  generations.  Heat  alone  is  perhaps  the  agent 
employed  by  nature  to  produce  these  incipient  organizations,  or  it 
may  act  in  concert  with  electricity.  M.  de  Lamarck  did  not  believe 
that  a  bird,  a  horse,  nor  even  an  insect,  could  directly  form  them- 
selves in  this  manner;  but,  in  regard  to  the  most  simple  living 
bodies,  such  as  occupy  the  extremity  of  the  scale  in  the  different 
kingdoms,  he  perceived  no  difficulty;  for  a  monad  or  a  polypus  are, 
in  his  opinion,  a  thousand  times  more  easily  formed  than  the  embryo 
of  a  chick.  But  how  do  beings  of  a  more  complicated  structure,  such 
as  spontaneous  generation  could  never  produce,  derive  their  existence? 
Nothing,  according  to  him,  is  more  easy  to  be  conceived.  If  the 
orgasm,  excited  by  this  organizing  fluid,  be  prolonged,  it  will  aug- 
ment the  consistency  of  the  containing  parts,  and  render  them 
susceptible  of  reacting  on  the  moving  fluids  which  they  contain,  and 
an  irritability  will  be  produced,  which  will  consequently  be  possessed 
of  feeling.  The  first  efforts  of  a  being  thus  beginning  to  develope 
itself  must  tend  to  procure  it  the  means  of  subsistence  and  to  form 
for  itself  a  nutritive  organ.  Hence  the  existence  of  an  alimentary 
canal.  Other  wants  and  desires,  produced  by  circumstances,  will 
lead  to  other  efforts,  which  will  produce  other  organs :  for,  according 
to  a  hypothesis  inseparable  from  the  rest,  it  is  not  the  organs,  that  is 
to  say,  the  nature  and  form  of  the  parts,  which  give  rise  to  habits 
and  faculties ;  but  it  is  the  latter  which  in  process  of  time  give  birth 
to  the  organs.  It  is  the  desire  and  the  attempt  to  swim  that  produces 
membranes  in  the  feet  of  aquatic  birds;  wading  in  the  water,  and 
at  the  same  time  the  desire  to  avoid  getting  wet,  has  lengthened  the 
legs  of  such  as  frequent  the  sides  of  rivers;  and  it  is  the  desire  of  flying 

222  EMBRYOLOGY   IN   THE    SEVENTEENTH       [pt.  ii 

that  has  converted  the  arms  of  all  birds  into  wings,  and  their  hairs 
and  scales  into  feathers.  In  advancing  these  illustrations,  we  have 
used  the  words  of  our  author,  that  we  may  not  be  suspected  either  of 
adding  to  his  sentiments  or  detracting  any  thing  from  them." 

If  the  latter  part  of  the  eighteenth  century  did  not  produce  the 
move  forward  in  the  morphological  direction  which  might  have  been 
expected  from  the  work  of  Wolff,  a  remarkable  amount  of  work  was 
accomplished  on  the  chemical  side.  This  mass  of  work  did  not  spring 
from  any  one  source,  it  was  not  due  to  a  great  discovery  on  the  part 
of  one  man,  but  rather  it  came  about  that,  as  the  technique  of 
chemistry  itself  improved,  a  number  of  otherwise  undistinguished 
investigators,  such  as  Dehne,  Macquer  and  Bostock,  applied  physico- 
chemical  methods  to  the  embryo,  though  it  is  true  that  among  the 
names  are  those  of  certain  great  chemists,  such  as  Scheele  and 
Fourcroy.  The  results  of  this  movement  were  summarised  in  the  work 
of  J.  F.John,  whose  Chemische  Tabellen  des  Tierreichs  appeared  in  1814. 
With  this  date  I  propose  to  bring  my  historical  assessment  to  an 
end.  The  work  that  was  done  in  physico-chemical  embryology 
after  181 4  will  be  considered  in  the  appropriate  sections  dealing 
with  the  problems  of  the  present  time;  for  Gobley,  as  an  example, 
who  gave  the  name  to  the  substance  still  called  vitellin,  was  working 
only  a  dozen  years  after  the  date  of  the  publication  of  John's 

In  this  translation  of  the  Tables,  I  have  made  one  alteration  only. 
John  groups  together  a  number  of  data  which  are  contained  in  von 
Haller's  Elementa  Physiologiae,  and  attributes  them  to  that  great  man. 
But  actually  they  were  obtained  by  earlier  investigators  and  only 
came  to  John  through  the  medium  of  Haller  and  Fourcroy — I  have 
therefore  allotted  them  to  their  true  originators. 


Substance  or  liquid 

investigated  Composition 

Amniotic  liquid  (man)        It  contains  a  substance  which  can  be 
precipitated  with  tincture  of  gall, 
phosphate  of  lime  and  muriatic  salts 
„  It  is  salt 

„  It  is  sweet 

,,  It  coagulates  on  boiling 













Barbati  & 



SECT.  3] 




Substance  or  liquid 

Amniotic  liquid  (man) 

Cheesy  material,  given 
off  into  the  amniotic 
liquid  by  the  body  of  the 
foetus  (man) 

Embryonic    tissue-juice 

Amniotic  liquid  (cow) 

Amniotic   and   allantoic 
liquids  (cow) 


It  is  miscible  with  water 
It  is  coagulable  by  tincture  of  gall 
It  is  coagulable  by  alcohol 
It  is  coagulable  by  alumina 
It  is  coagulable  by  spirits  of  nitre 
Free  mineral  alkali,  water,  albumin- 
ous substance,  common  salt 
Much   water,   very    little    common 
salt,   fire-stable  alkali,  phosphoric 
acid,   some    earth,   and   oxyde    of 

Much  water,  a  lymphatic  coagulum, 
common  salt,  salmiac,  a  trace  of 
phosphate  of  lime 
Sp.  g.  1-005.  Albuminous  matter, 
soda,  muriate  of  soda,  phosphate  of 
lime,  the  rest  is  water 

Animal  slime,  and  a  characteristic 
fatty  material,  or  rather  an  albu- 
minous material  tending  to  fat,  car- 
bonate of  lime 

It  contains  hydrofluoric  acid 

Water,  much  sulphate  of  soda, 
phosphate  of  lime  and  talc,  an 
animal  substance  soluble  in  water, 
insoluble  in  spirits  of  wine,  and 
not  forming  a  combination  with 
tannic  acid,  a  crystalline  amniotic 

The  liquid  of  the  allantois  is  very 
different  quantitatively  in  the  dif- 
ferent periods  of  pregnancy,  as  also 
in  the  qualitative  aspect  of  its  com- 
position. First  it  is  crystalline  and 
colourless,  then  it  gets  yellowish, 
and  finally  a  dark  reddish-brown. 
But  it  remains  watery  all  the  time 
and  never  has  the  property  possessed 
by  the  amniotic  liquid,  of  becoming 
at  last  quite  slimy  even  to  the  point 
of  showing  fibres  in  it.  During  the 
last  months  the  hippomanes  appear 
in  it,  these  are  soft  and  yet  tough. 
The  quantity  of  this  liquid  is  much 
greater  at  the  end  than  at  the  be- 
ginning. Alcohol  precipitates  from 
it  a  very  large  amount  of  a  reddish 
substance;  sulphate  of  baryta,  tar- 
taric acid,  and  carbonate  of  lime 
give  a  large  precipitate.  These  re- 
agents do  not  change  the  amniotic 
fluid  at  all.  1000  gm.  Uq.  allant. 
gave  20-25  gm.  solid  residue, 
1000  gm.  liq.  amnii  gave  lo-i  i  gm. 
solid  residue 













Gmelin  & 



van  den  Bosch 



Vauquelin  & 

Vauquelin  & 


Buniva  & 





EMBRYOLOGY    IN   THE   SEVENTEENTH       [pt.  ii 


Substance  or  liquid 

Blood  of  embryo  (man) 

Blood  of  embryo  (rabbit) 

Foetal  urine  (man) 
Meconium  (man) 

Meconium  (cow) 

Eggs  (wild  birds) 





Composition  Investigator 

Soda,  much  serum,  and  some  leathery     Fourcroy 

fibrous    threads,    which    made    up 

only  ^  grain  out  of  3  gros  6  grains 

of  cruor .  They  were  jelly-like  in  con- 
sistency.   No  phosphoric  acid.    It 

differed  from  the  blood  of  an  adult 

(i)  in  not  giving  a  red  flush  when 

shaken  up  with  air,  (2)  in  not  clot- 
ting in  air,  (3)  in  the  fibres  being 

more  jelly-like 
Does  not  coagulate  in  the  cold  but     Fourcroy 

gives  rise  to  a  red  serum  tending 

towards  brown.   It  was  not  as  solid 

as  usual  except  when  heated,  then 

it  went  grey  though  the  supernatant 

liquor  was  red 
It  is  odourless  and  colourless  and  of    Fourcroy 

a  slimy  nature 
Water  f ,  ^r>  spirituous  extract  similar     Bay  en 

to  gall,  a  black  residue  dissolving 

partially  in  water  to  give  a  yellow 

colour.    He  holds  it  to  be  a  milky 

Contains  true  gall-like  substances 



Does  not  contain  air  of  different  com- 
position from  atmospheric  air 

Phosphate  of  lime,  animal  glue,  and 
some  combustible  substance  which 
escapes  with  a  sulphurous  smell 
from  shells  when  they  are  softened 
in  acid.  Ferrous  particles.  Some- 
times some  common  salt.  An  egg, 
which  weighed  2  ozs.  2  scruples  15 
grains,  had  white  which  weighed 
10  qentchen  2  scruples,  yolk  ^  oz. 
\  scruple,  and  shell  and  membranes 
2  drachms  5  grains 

An  animal  material  insoluble  in  acids 

6  qentcfwn  2  scruples  7  grains  lost 
practically  6  qentchen  in  drying,  it 
contains  no  caustic  salts,  the  ash  is 
an  earthy  insipid  dust 

Albuminous  matter,  water,  muriate 
of  soda,  phosphate  of  lime,  and 

Albuminous  matter,  oil,  yellow  pig-     Adet 

From  60  eggs,  5^  ozs.  oil  Dehne 

Albuminous     matter     with     much     Adet 

Carbonate  of  lime,  phosphate  of  lime,     Adet 
and     very     oxydised     albuminous 

Buniva  &  — 

Hehl  1 796 

von  Wasserberg  1 780 

von  Wasserberg    1 780 
von  Wasserberg    1 780 


SECT.  3] 



Substance  or  liquid 


Eggs  (domestic  hen) 

Investigator       Date 


A  fine  earth  and  a  gelatinous  material 
True  lime,  containing  perhaps  phos- 
phoric acid 
\  oz.  of  pulverised  clean  shell,  di- 
gested with  spirits  of  wine,  gave  i  \ 
grains  of  an  extract  which  smelt  and 
tasted  rancid.  The  same  amount  of 
shell  gave    i    scruple   of  a  yellow 
watery  extract  which  tasted  salt 
Carbonate  and  phosphate  of  lime, 
traces  of  a  jelly,  which  can  be  used 
as  gum.    Phosphoric  acid  can  be 
had  from  the  ash 
Carbonate  and  phosphate  of  lime, 
bitter  earth  and  iron,  a  jelly  which 
can  be  used  as  gum 
Carbonate  of  Hme  72  parts,  phos- 
phate of  lime  2,  jelly  3,  water  and 
loss  23 
Carbonate  of  lime  89-6  parts,  phos- 
phate of  lime  5-7,  animal  substance 
4-7,  traces  of  sulphur.  As  a  hen  lays 
130  eggs  in  six  months  and  as  an 
egg  weighs  on  an  average  58-117 
grams,  7486-226  grams  of  solid  must 
be  used  for  egg-production  in  that 
time,   i.e.   since   the   shells   would 
weigh  64-685  gm.,   7333-793  gm., 
14    pounds    15    ounces    7    gros    8 
grains.  The  secretion  of  the  lime  is 
probably  accomplished  by  means 
of  the  kidneys 
Carbonate  and  phosphate  of  lime, 
and  jelly 
Very  much  carbonate  of  lime,  very 
little   phosphate.   Traces   of  phos- 
phate  of  iron,   earthy  carbonates, 
rnuriates,    albuminous    and    gela- 
tinous substance  to  hold  it  together. 
I  cannot  find  any  uric  acid  in  it,  as 
Vauquelin  says  is  there,  nor  is  he 
right  in  saying  that  the  sulphur  is 
in  the  shell — it  is  in  the  membranes 
only,  and  under  the  form  of  sul- 
phuric acid 

Consist  of  an  animal  material 
Have  the  properties  of  the  fibrous 

part  of  blood 
A  jelly-like  material,  soluble  in  hot 

An  animal  substance  with  traces  of 

phosphate   of  lime,    carbonate   of 

lime,  muriates,  and  a  sulphurous 

An  albuminous  substance  containing 

traces   of  sulphur   and   soluble   in 

caustic  potash 





1 781 



Merat-Gaillot     — 

Vauquelin  1 799 








Vauquelin  — 


226  EMBRYOLOGY   IN   THE   SEVENTEENTH       [pt.  ii 


Substance  or  liquid 





Egg  (Snipe,  Tringa  vanellus) 


An  agglutinative  substance  insoluble 
in  water,  apparently  like  dried  tra- 
gacanth  gum 

A  white  lymphatic  transparent  sticky 
slimy  material 

Soda,  albuminous  matter,  water, 

Water,  albuminous  matter,  with 
some  free  alkali,  phosphate  of  lime, 
muriate  of  soda,  and  sulphur 

Contains  benzoic  acid 

Water  80  parts,  uncoagulable  sub- 
stance 4-5  parts,  albuminous  matter 
15-5  parts,  traces  of  soda,  sul- 
phuretted hydrogen  gas,  and  ben- 
zoic acid 

Contains  sulphur 

Water,  albuminous  matter,  a  little 
jelly,  soda,  sulphate  of  soda,  muriate 
of  soda,  phosphate  of  lime,  oxyde 
of  iron  (?) 

An  oxydised  albuminous  substance 
Apparently  an  albuminous  substance 

Consists  of  a  lymphatic  material  and 

a  fatty  oil 
Water,  oil,  albuminous  matter,  jelly 
Water,  oil,  albuminous  matter,  jelly, 
phosphates  of  lime  and  soda,  with 
other  salts 
Water,  oil,  albuminous  matter 
Water,  a  mild  oil,  albuminous  matter, 
a  colouring  matter  which  is  perhaps 
Water,  a  yellow  mild  oil,  traces  of  free 
(phosphoric?)  acid,  a  small  amount 
of  a  reddish-brown  material,   not 
fatty,  and  soluble  in  ether  and  warm 
alcohol,   a  jelly-like   substance,    a 
great  deal  of  a  modified  albuminous 
substance,  and  sulphur 

Egg  (lizard,  Lacerta  viridis) 


Egg  (fish,  salmon) 

Is  composed  of  the  same  constituents 
as  that  of  the  hen,  but  the  dark 
green  pigment  and  the  dark  brown 
splashes  are  probably  oxyde  of  iron 

A  yellow  oil,  an  albuminous  material, 
and  salts 

Diflfers  from  that  of  fowls  in  being 
granular  and  greasy  when  hardened 
by  boiling 

420  grains  contained  of  pure  dry 
albuminous  matter  26  grains,  of  a 
viscous  oil  18  grains,  insoluble  al- 
buminous matter  102  grains,  mu- 












Fourcroy  — 

John  — 

Macquer  1781 

Thomson  — 

Hatchett  — 

Jordan  — 

Fourcroy  — 








Substance  or  liquid 

investigated  Composition  Investigator      Date 

riate  of  soda  and  sulphuric  alkali 
28  grains,  jelly,  phosphate  of  lime, 
and  oxyde  of  iron  2  grains,  water 
242  grains 

Egg  (fish,  Cyprinus  barbiis)     Contains  a  substance  dangerous  for  Crevelt  — 

man,  the  nature  of  which  is  unknown 

Egg  (insect,  Locusta  viridissima,  and  migratoris) 

Shell  An    animal    combustible    substance  John  — 

and  phosphate  of  lime 

Contents  Albuminous  matter,  a  yellow  fluid  John  — 

fatty  oil,  a  little  jelly  and  a  charac- 
teristic substance,  acid,  phosphates, 
and  sulphuric  alkali 

The  most  interesting  of  the  investigators  in  this  table  is  Dzondi, 
whose  work  in  1806  was  the  first  in  which  definite  chemical  charac- 
teristics were  systematically  followed  throughout  embryonic  develop- 
ment. It  is  surprising  that  so  long  a  time  should  have  elapsed  between 
Walter  Needham  and  John  Dzondi:  no  less  than  139  years. 

After  1 8 14  events  were  to  move  so  rapidly  in  the  world  of  science 
that  it  would  not  be  possible  to  follow  all  the  embryological  work 
that  was  done,  and  at  the  same  time  maintain  the  proper  proportion 
between  the  historical  part  of  this  book  and  the  other  parts.  The 
eighteenth  century  was  the  period  during  which  the  chemical  side 
of  embryology  began  to  differentiate  and  split  itself  off  from  the  rest. 
After  1 8 14  it  pursued  a  course  of  its  own,  the  individual  tracks  of 
which  I  shall  mention  under  their  appropriate  heads.  But  another 
century  had  yet  to  pass  before  the  value  of  the  physico-chemical 
approach  to  embryology  could  become  generally  recognised,  and  we 
are  ourselves  only  at  the  very  beginning  of  this  new  period. 

A  certain  contrast  may  appear  between  the  critical  treatment 
which  I  have  given  to  the  investigators  whose  work  I  have  been 
discussing,  and  the  saying  of  William  Harvey's — "all  did  well", 
which  stands  prefixed  to  this  Part  of  the  book.  Yet  history  without 
criticism  is  a  contradiction  in  terms,  and  the  praise  and  dispraise, 
which  I  have  tried  to  allot  as  accurately  and  justly  as  I  could,  is, 
as  it  were,  technical,  rather  than  spiritual.  All  the  workers  who  have 
been  mentioned,  and  others  besides  them  who  left  no  special  marks 
on  their  time,  are  worthy  of  our  respect  and  of  our  fullest  praise, 
for  they  preferred  wisdom  before  riches  and,  according  to  their 
several  abilities  and  generations,  diligently  sought  out  truth. 



All  things  began  in  order,  so  shall  they  end,  and 

so  shall  they  begin  again,  according  to  the  ordainer 

of  order  and  the  mystical  mathematicks  of  the  city 

of  heaven. 

Sir  Thomas  Browne. 


There  have  already  been  certain  reviews  of  work  in  chemical  embryo- 
logy as  a  whole,  among  which  those  of  Paechtner  and  Schulz  are 
the  most  valuable.  The  former  dealt  almost  exclusively  with  the 
chemistry  of  the  egg  from  a  static  viewpoint,  and  only  devoted  a 
short  section  to  the  metabolism  of  the  embryo  during  its  develop- 
ment, while  the  latter,  though  dealing  specifically  with  embryonic 
metabolism,  gave  hardly  more  space  to  it  than  Paechtner.  In  both 
cases  the  discussion  was  little  more  than  a  catalogue  of  references, 
and  in  neither  case  was  the  literature  anything  like  complete,  in- 
cluding, indeed,  less  than  a  tenth  of  the  relevant  citations. 

The  first  review  of  chemical  embryology  was  written  by  Grafe  in 
19 10,  but,  though  he  outlined  several  valuable  ideas,  it  is  now  of 
small  importance.  Good  information  may,  however,  be  found  in 
Aron's  monograph  on  the  chemistry  of  growth  and  on  the  mammalian 
side  there  are  Harding  and  Murlin.  Other,  less  satisfactory,  reviews 
are  by  Cazzaniga  and  Steudel.  Finally  there  is,  of  course,  an 
immense  amount  of  work  which  can  be  found  in  no  review,  for 
investigators  have  followed  the  counsel  of  Godlevski  (1910):  "Un- 
sere  Kenntnisse  hinsichtlich  der  chemischen  Zusammensetztung  der 
Eier  noch  lange  nicht  ausreichend  sind,  so  waren  weitere  Forschungen 
auf  diesem  Gebiete  auch  aus  dem  Grunde  sehr  erwunscht  weil  sie 
den  Ausgangspunkt  fiir  die  Physiologic  des  embryonalen  Stoff- 
wechsels  welcher  bisher  gleichfalls  nur  sehr  wenig  untersucht  wurde, 
bilden  mussen". 

Every  effort  has  been  made  to  give  an  accurate  and  complete 
presentation  of  the  data  in  the  Tables  of  this  book  and  of  the 
experimental  conditions  under  which  they  were  obtained,  but 
investigators  should  always  consult  in  addition,  whenever  possible, 
the  relevant  original  memoirs  referred  to  in  the  Bibliography. 



I -I.    Introduction 

In  giving  an  account  of  the  present  state  of  our  knowledge  about  the 
chemical  constitution  of  the  egg-cell  and  the  food-material  which  is 
accumulated  around  it  or  inside  it,  I  shall  not  follow  a  strictly  logical 
order  of  exposition,  according  to  the  phyla  of  systematic  biology. 
I  have  judged  it  best  to  begin  with  the  egg  of  the  hen,  for  not  only 
is  it  the  most  familiar  and  the  best  known  of  all  eggs,  but  it  is  also 
the  one  which  has  been  most  thoroughly  investigated  biochemically. 

It  should  be  remembered  that  the  two  main  morphological  divisions 
of  the  egg,  (a)  the  egg-cell  itself  and  {b)  its  coverings,  appear  in 
protean  modifications  throughout  the  animal  kingdom.  The  former 
may  be  a  simple  cell  with  its  ooplasm,  nucleus,  nucleolus,  etc.,  as  in 
the  echinoderms,  and  no  covering  at  all  save  its  cell-membrane,  or 
at  the  other  extreme  it  may  be  swollen  up  with  food-material  or  yolk 
to  the  prodigious  proportions  of  the  avian  egg-cell.  The  membrane 
again  may  be  a  thin  coat  of  investing  cells  such  as  the  tunicate  egg 
possesses,  or  it  may  be  the  jelly  of  the  amphibian  egg,  or,  again,  it 
may  be  the  complex  arrangement  of  egg-white,  chalazae,  shell- 
membranes,  and  shell,  which  is  present  in  the  bird's  egg.  All  imagin- 
able degrees  of  richness  in  yolk  are  present  in  the  egg-cells  of  animals, 
and  upon  this  fact  depend  the  various  kinds  of  cleavage  which  they 
show:  alecithic  eggs,  on  the  one  hand,  such  as  those  of  most  inverte- 
brates, having  a  holoblastic  form  of  development  in  which  the  whole 
egg  participates  in  cleavage;  and  yolk-rich  eggs,  on  the  other  hand, 
such  as  those  of  most  vertebrates,  having  a  meroblastic  development, 
only  a  localised  part  of  the  egg  undergoing  cleavage,  the  rest  remaining 
as  a  sac  full  of  yolk  until  it  is  finally  absorbed. 

1-2.    General  Characteristics  of  the  Avian  Egg 

After  the  historical  introduction  which  has  been  given,  it  should  be 
unnecessary  to  remark  on  the  general  arrangement  of  the  bird's  egg. 
We  have  with  Harvey  referred  to  it  as  an  exposed,  and,  as  it  were, 
detached  uterus,   and  with  Fabricius  ab  Aquapendente  we  have 


enumerated  the  parts  of  the  typical  avian  ovum.  Fig.  13,  however, 
shows  the  general  disposition  of  parts  diagrammatically. 

First,  as  to  size  and  shape.  The  size  and  shape  of  the  egg  were  shown 
by  Curtis  in  191 1  and  by  Surface  in  191 2  to  be  due  partly  to  the 
structure  of  the  oviduct,  which  very  probably  may  be  considered  an 
inherited  character,  as  was  claimed  by  Newton.  D'Arcy  Thompson's 
discussion  of  the  mechanics  of  egg-formation  in  birds,  in  his  Growth 

"  White  or  Milky  Yolk 

\     Germinal  Di^c         .Pander's  Nucleus 
Shell  -Membranes      ^ ^   ' t-  _ ,  ^ 



Chalazae  ^^^^^^'^  '  "^  ...^'^  ^ 

(Treadles,  HailstOTie^r^^^::;^^^  I  ^       ^^^^^^'^  ^,     \ 

y,      ^^=^^^^^— 1-______-^^^^^'^        Chalazae 

/■  «r~     I  ^;  ^ 

Vitelline  Membmne  Haloes  or  ^ 

Layers  of  Yellow  Yolk       ^Whi  te 

Fig.  13.  Diagrammatic  representation  of  the  hen's  egg.  The  chalazae  were  called  by 
Tredern  Ligamenta  albuminis.  Bartelmez  gives  a  discussion  of  the  factors  governing 
the  angle  which  the  embryonic  axis  makes  with  the  axis  of  the  egg  as  a  whole.  The 
yolk  is  not  a  perfect  sphere  but  lengthened  along  the  main  axis.  The  egg-white 
is  divisible  into  three  layers  which  increase  in  density  from  without  inwards.  The 
chalazae,  as  Berthold  was  the  first  to  find,  are  not  present  in  reptilian  eggs. 

and  Form,  will  be  famiHar,  but  some  biologists,  such  as  Horwood, 
have  taken  exception  to  his  conclusions  about  the  physical  influences 
which  shape  the  egg.  Ernst's  well-known  experiment  was  the  starting- 
point  of  these  discussions ;  she  caused  hens  to  lay  on  a  surface  of  wet 
sand  and  charcoal,  and  so,  observing  the  process,  found  the  blunt  end 
to  be  blackened.  This  was  in  agreement  with  many  other  observers, 
such  as  V.  Nathusius;  Landois;  Jasse;  Konig-Warthausen  and  Erd- 
mann;  and  d'Arcy  Thompson  accordingly  described  the  hen's  egg 
as  moving  down  the  oviduct  blunt  end  forwards,  the  pointed  end 
owing  its  form  to  the  peristaltic  compression  of  the  oviduct.    Unfor- 

234  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

tunately  all  observers  agree  (Purkinje;  von  Baer;  Coste;  Kiitter; 
Taschenberg;  Wickmann  and  Patterson  for  the  hen,  Blount  and 
Patterson  for  the  pigeon,  Kiitter  for  the  hawk,  and  Wickmann  for 
the  canary)  that  the  pointed  end  passes  first  down  the  oviduct.  It 
appears  that  the  egg  must  turn  right  round  in  the  act  of  being  laid, 
and  Bartelmez,  indeed,  has  seen  this  occur.  Curtis  has  shown  that 
the  shape  of  the  egg  depends  to  some  extent  upon  its  size  and  this 
biometric  observation  was  afterwards  confirmed  by  Pearl  &  Curtis. 
Many  abnormalities  have  been  reported  in  eggs.  They  need  merely 
be  mentioned  here  with  their  authorities,  thus : 





Eggs  containing  masses  of  tissue^  more  or  less  organised. 

von  Nathusius. 



Dwarf  eggs. 

Pearl  &  Curtis. 



Ovum  in  ovo. 






Pearl  &  Curtis. 



Roberts  &  Card. 


Double  and  triple-yolked  eggs. 


Parker.  ' 




Inadequate  shell. 

Riddle  &  King. 

Dwarf  or  absent  yolk  (ovum  centennium^). 


^  See  Sir  Thos.  Browne,  Pseudodoxia  Epidemica,  Bk  iii,  ch.  7,  "Of  the  basilisk".  The  eggs 
of  Chelonia  also,  according  to  Deraniyagala,  are  sometimes  laid  without  yolks. 


It  is  interesting  in  this  connection  that  Riddle  has  traced  the 
occasional  production  of  eggs  with  deficiency  of  white  and  shell  but 
not  of  yolk,  to  a  lack  of  the  thymus  hormone  which  he  has  called 
"Thymovidine".  Feeding  with  desiccated  thymus  removed  com- 
pletely these  effects.  "The  whole  of  the  data",  he  said,  "seem  to 
demonstrate  the  presence  in  the  thymus  of  a  substance  having  a  highly 
specific  action  on  the  oviduct  of  birds — and  presumably  on  that  of  all 
those  vertebrate  animals  which  secrete  egg-envelopes."  The  syndrome 
involved  eggs  with  normal  yolks  but  hardly  any  shell  or  albumen, 
frequent  reduction  of  normally  paired  ovulations  to  single  ovulations, 
diminished  fertility,  and  restricted  hatchability  of  the  eggs.  "Though 
not  necessary  to  the  life  of  the  individual",  said  Riddle,  "thymo- 
vidine would  seem  to  be  essential  to  the  perpetuation  of  those  verte- 
brate species  whose  eggs  are  protected  by  egg-envelopes.  Such 
animals  were  the  ancestors  of  mammals  and  thus  mammals  could 
hardly  have  come  into  existence  without  the  thymus."  These  con- 
siderations are  of  much  interest  in  view  of  other  speculations  on  the 
evolutionary  aspect  of  chemical  embryology,  e.g.  Section  6-6.  They 
also  suggest  that  the  mammalian  thymus  is  now  a  vestigial  organ. 

The  air-space,  the  shell  and  the  white  of  the  normal  egg  need  no 
special  remark  at  present,  but  the  yolk  is  a  more  complicated  structure. 
Around  a  central  core  of  "white"  or  "milky"  yolk  the  yellow  yolk  is 
secreted  in  the  ovary  of  the  hen  in  concentric  layers,  which  form  the 
appearance  of  "haloes"  in  the  finished  egg,  and  which  show  up  es- 
pecially clearly  when  the  hen  is  fed  on  Sudan  III  or  some  other  non- 
toxic dye  which  has  a  selective  staining  action  on  fat.  The  white  yolk 
in  the  centre  is  continued  in  a  flask-like  shape  (the  latebra)  up  to  the 
surface  of  the  yolk  underneath  the  germinal  disc,  and  is  then  con- 
tinued in  a  very  thin  layer  all  round  the  exterior  of  the  yolk  under- 
neath the  vitelline  membrane.  The  white  yolk  is  thus  the  first 
nourishment  of  the  embryo.  It  is  not  certain  whether  there  are 
also  layers  of  white  yolk  between  the  concentric  layers  of  yellow  yolk, 
for  they  have  never  been  analysed  chemically,  and  Balbiani  main- 
tains that  they  only  differ  from  the  yellow  layers  by  having  less  yellow 
pigment.  The  differences  between  the  true  white  yolk  and  the  yellow 
yolk  are,  as  will  be  seen  later,  far  more  profound.  Balfour  & 
Foster,  in  their  Elements  of  Embryology  of  1877,  described  the  yellow 
yolk  as  consisting  histologically  of  spheres  of  from  25  to  loo/x  in 
diameter,  filled  with  numerous  minute  highly  refractive  granules  and 



[PT.  Ill 

very  susceptible  to  crushing  and  rough  treatment.  After  boihng,  the 
spheres  assume  a  polyhedral  form.  The  granules  seen  within  them  must 
consist  of  protein,  for  they  are  not  soluble  in  ether  or  alcohol.  On  the 
other  handjthe  white  yolk  elements  are  vesicles  smaller  than  the  globules 
of  the  yellow  yolk,  being  about  4  to  75  /n  across,  with  a  highly  refractive 
body,  often  as  small  as  i  [x,  in  the  interior  of  each.  These  vesicles  are 
sometimes  collected  together  into  much  larger  vesicles.  They  observed 
also  underneath  the  blastoderm  or  the  germinal  disc  a  number  of 
large  vacuoles  filled  with  fluid — large  enough,  in  fact,  to  be  seen  with 
the  naked  eye.  The  histology  of  yolk  has  been  reviewed  by  Dubuisson, 
and  at  one  time  many  papers  were  published  on  it,  e.g.  those  of 
Virchow.  They  cannot  be  considered  in  detail  here. 

1-3.    The  Proportion  of  Parts  in  the  Avian  Egg 

Of  the  weight  of  the  whole  egg,  the  shell  takes  up  about  10  per 
cent.,  the  albuminous  white  50  per  cent,  and  the  yolk  30  per  cent, 
in  round  numbers.  These  relationships  have  been  determined  by  a 
multitude  of  investigators,  whose  results  are  drawn  up  in  Table  i . 

Table  i .   Distribution  of  the  parts  in  the  egg, 

Italic  figures  represent  dry  weight  only. 


egg  weights 










and  date 

Hen,  Polish  i 





van  Hamel-Roos  ('.890) 

,,     Polish  ii 






,,     Holland  (Zwol.) 






„     Holland  (Tiel) 











Miinster  Ag.  Sta.  (1900) 






Drechsler  (1896) 












Plimmer  (1921) 



I  i-i 








Langworthy  (190 1-2) 
































Lebbin  (1900) 





Welmanns  (1903) 






Segin  (1906) 






Liihrig  (1904) 







Hen  (various  breeds) 





von  Czadek  (191 7) 





Rose  (1850) 







Hen  (various  breeds) 





Carpiaux  (1903) 






Lehmann  (1850) 






Prout  (1859) 






Poleck  (1850) 



Stained  by  Kossa's  method  for  the  detection  of  calcium  phosphate.  The  considerable 
variations  in  the  vitelline  globules  may  be  noted.  Magnification,  6xD:  prepared  and 
microphotographed  by  Dr  V.  Marza. 



SECT.    l] 



Table  i  {cont.) 


egg  weights 










and  date 

Hen,  Leghorn 





Murray  (1925) 

Hen  (various  breeds) 





Iljin  (1917) 












van  Meurs  (1923) 












Voit  (1877) 

Nidicolous  birds 






Tarchanovf  (1884) 

Starling    ... 


















Canary     ... 






Thrush     ... 





J  J 


















Nidifugous  birds 

























Turkey     ... 























Glikin  (1908) 






Davy  (1863) 



























3  J 

Golden-crested  wren 





) ) 




















J  J 






J  J 





















Hartung  (1902) 





Voit  (1881) 



Fere  (1896) 











Pott  &  Preyer  (1882) 






Rozanov  (1926) 






Hepburn  &  Katz  (1927) 











Baudrimont  &  de 
St  Ange  (1846) 

Dwarf  hen  ... 





Sacc  (1847) 




Pott  (1879) 





Atwater  &  Bryant  ( 1 906) 


■f-  All  Tarchanov's  figures  exclude  the  shell  weight. 



[PT.  Ill 

Table  i 


Weight  of 








tents  (gm.) 





and  date 


•        57-12 





Friese  (1923) 


•      137-38 






781 1 






•        92-93 


















•        25-40 












.        27-03 





Blackbird     ... 
















Weight  of 








ents  (gm.) 




and  date 

Plover  ( Vanellus  crist 






Bauer (1893-5) 

Hen  {Gallus  domestict 







Guinea-fowl  {Meleag 

ris  gallopavo) 





Swallow  (Hirundo  ru. 






Partridge  [Perdrix  ci 






Sparrow  {Passer  dom 






Thrush  (Turdus 

?        )      ... 





Duck  (Anas)  [doubl 






The  above  data  were  all  obtained  without  any  ad  hoc  investigation  of  the  probable 
errors  involved  in  weighing  eggs  and  parts  of  eggs.  An  elaborate  study  by  M.  R.  Curtis 
in  1 9 1 1  gave  the  following  results  on  Gallus  domesticus : 

weight  in  gm.  % 

56-04  100 

33-22  59-26 

16-31  29-14 

6-28  ii-i8 

0-23  0-42 

Whole  egg 


Shell  and  membranes 

But  though  this  is  the  case  with  the  egg  in  its  natural  state,  the  solid 
matter  is  concentrated  much  more  in  the  -yolk  than  in  the  white, 
so  that,  as  the  analyses  of  Poleck  and  Iljin,  for  instance,  show,  for 
dry  weight  the  conditions  are  exactly  reversed.  The  egg-white  may, 
indeed,  be  regarded  as  the  principal  reservoir  of  water  for  the  embryo 
which  develops  on  dry  land,  and  this  is  a  point  which  will  be  dis- 
cussed later  (see  Section  6-6).  The  eggs  of  different  breeds  of  hen 
vary  to  some  extent  in  the  relative  weights  of  shell,  white  and  yolk; 
but,  although  it  is  difficult  to  lay  down  any  general  rule,  these  varia- 
tions do  not  greatly  exceed  the  variations  due  to  factors  connected  with 
the  individual  hen.  Iljin's  lightest  shells  make  up  about  7  per  cent, 
of  the  G,gg  weight  and  the  heaviest  not  more  than  11-5  per  cent. 


It  is  certain  that  there  are  constant  differences  between  the  eggs  of 
different  breeds,  but  as  a  whole  these  are  quite  outweighed  by 
individual  differences,  and  only  appear  when  extended  statistical 
studies  are  undertaken.  The  eggs  of  other  birds,  however,  do  not  fall 
within  these  limits.  Langworthy,  for  example,  has  shown  that,  in 
the  duck's  egg,  the  shell  may  account  for  as  much  as  14  per  cent, 
of  the  whole  weight.  A  similar  result  was  found  for  the  turkey  and 
the  goose,  while  the  guinea-fowl's  egg  has  a  shell  of  nearly  1 7  per 
cent,  of  the  whole  weight.  The  wide  series  of  Friese,  shown  in  Table  i, 
seems  to  indicate  that  the  larger  the  egg  the  more  shell  it  has  to 
have :  thus  the  canary's  egg  weighing  just  under  2  gm.  has  4  per  cent, 
while  the  goose's  egg  which  weighs  137  gm.  has  14  per  cent.  Heinroth, 
and  Groebbels  &  Mobert,  among  others,  have  collected  a  great 
many  data  of  this  kind  for  all  varieties  of  bird,  but  their  papers  must 
be  referred  to  for  the  figures.  Thus  the  fertilised  embryo  starts  its 
development  on  the  surface  of  a  mass  of  food  only  slightly  diluted 
with  water,  and  surrounded  by  a  further  and  much  wetter  supply. 
This  is  reflected  well  by  the  work  of  Bellini,  who  found  that  the  yolk 
of  the  hen's  egg  was  seven  times  as  viscous  as  the  white  at  the  begin- 
ning of  development.    (Alb.  3-4  units,  yolk  28-5  units.) 

A  good  deal  of  work  has  been  done  on  the  variability  of  the 
weights  of  the  parts  of  the  egg  within  a  given  species  of  fowl.  Thus 
Jull  found  that  egg  weight  is  the  least  variable  factor,  albumen 
weight  slightly  more  variable  than  egg  weight,  yolk  weight  con- 
siderably more  variable  than  albumen  weight,  and  shell  weight  the 
most  variable.  It  would  seem,  therefore,  as  if  a  compensatory  process 
takes  place  during  egg-production,  the  largest  yolks  having  the 
smallest  whites,  since  the  weights  of  the  entire  eggs  do  not  vary  as 
much  as  the  weights  of  the  components.  On  the  other  hand,  the 
smaller  eggs  contain  the  highest  percentage  of  albumen  and  shell 
and  the  lowest  percentage  of  yolk.  Jull  also  studied  closely  the 
seasonal  variations,  which  may  be  quite  considerable,  finding  that 
the  component  parts  of  the  egg  contribute  in  different  degrees  at 
different  times  of  the  year  towards  the  total  egg  weight.  The  question 
as  to  which  part  of  the  egg  is  mainly  responsible  for  large  or  small 
eggs  is  still  debated,  for  Curtis  concluded  from  his  observations  that 
it  is  the  egg-white,  while  Atwood  found  many  indications  contrary 
to  this.  Statistical  studies  on  the  egg  of  the  tern  have  been  made  by 
Rowan,  Parker  &  Bell;  Rowan,  Wolff,  Sulman,   Pearson,  Isaacs, 



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SECT.    l] 





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242  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

Elderton  &  Tildesley;  and  by  Watson,  Watson,  Pearson,  Karn, 
Irwin  &  Pearson. 

The  division  of  birds  into  the  two  classes  of  nidicolous  (those 
which  hatch  as  squabs)  and  nidifugous  (those  which  hatch  as  downy, 
feathered  and  active  chicks)  has  been  shown  to  extend  to  the  com- 
position of  their  eggs  by  several  investigators.  Davy  found  that  the 
eggs  of  the  nidicolous  birds  had  thinner  and  more  fragile  shells, 
which  took  up  a  less  proportion  of  the  weight  of  the  whole  egg  than 
the  shells  of  nidifugous  birds.  Thus  the  wren's  egg-shell  weighs  only 
5  per  cent,  of  the  whole  egg  weight,  while  the  hen's  weighs  lo  per 
cent.  Da\y's  figures  show  very  clearly  that  the  main  reservoir  of 
solid  is  the  yolk  and  the  main  reservoir  of  water  is  the  egg-white. 

Tarchanov  carried  the  matter  further,  and  observed  that  the  yolks 
of  nidicolous  birds  always  formed  a  smaller  proportion  of  the  total 
amount  of  material  inside  the  egg  than  in  nidifugous  birds.  Thus, 
for  the  former  class  the  egg-white  accounts  for  about  78  per  cent, 
of  the  egg  and  the  yolk  for  22  per  cent.,  while,  in  the  latter  class, 
the  egg-white  accounts  for  about  55  per  cent,  and  the  yolk  for  45. 
All  these  differences  are  probably  related  to  the  shorter  incubation- 
time  of  the  nidicolous  eggs;  and,  as  will  be  seen  later,  there  are  not 
wanting  indications  that  the  yolk  of  these  is  less  tightly  packed  with 
food-material  and  more  rich  in  phosphatides. 

1*4.   The  Chemical  Constitution  of  the  Avian  Egg  as  a  whole 

The  composition  of  the  egg  as  a  whole  is  further  considered  in 
Table  2,  where  it  is  noticeable  that  the  analyses  of  water  and  ash 
have  not  been  significantly  improved  upon  between  1863  (the  date 
of  the  first  analysis,  Payen's)  and  the  present  time.  The  later  figures 
for  protein  and  fat  are,  however,  much  the  more  reliable.  It  should 
be  observed  that  there  is  an  approximately  equal  quantity  of  fat  and 
protein  at  the  disposal  of  the  embryo,  though  the  former  is,  of  course, 
in  the  yolk,  and  the  latter  is  preponderantly  in  the  egg-white.  This 
protein-fat  equality  is  by  no  means  the  rule  in  all  eggs,  and,  as  we 
shall  see  later,  the  eggs  of  fishes  depart  widely  from  it.  There  appear 
to  be  only  small  differences  between  the  eggs  of  different  kinds  of 
birds  in  protein  content.  At  one  time  it  was  thought  that  the  duck's 
egg  was  particularly  rich  in  fat,  on  the  authority  of  Commaille's 
analyses,  but  Liihrig  has  since  then  brought  it  into  line  with  all  the 
others.    It  does  seem,  however,  to  have  a  considerably  higher  per- 





centage  of  mineral  substances  than  the  rest.  The  dry-weight  figures 
merely  demonstrate  again  the  approximate  equality  of  the  protein 
and  fat. 

Before  we  proceed  to  consider  the  parts  of  the  tgg  in  separation, 
the  question  of  individual  and  racial  differences  must  be  taken  up 

Table  3.    Individual  differences  between  hen's  eggs, 
Malcolm's  figures  (1902).   Averages  of  individual  hens. 

Breed  unknown 

Italian  hens  (fed  on  maize  and  barley) 

From  one  hen 

From  one  hen 

Iljin's  figures  (19 17). 

Plymouth  Rock 
Rhode  Island  .. 

itty  acids 




















I  52 






















30- 1 2 







%  dry  weight 


Lecithin  P 











59- 1 6 



Table  4.    Race  differences  in  hen's  eggs. 

Leveque  &  Ponscarme's  figures. 


%  of  egg  d. 

"y  weigh 



dry  weight 



of  whole 



N  in 



i>  111 





in  yolk 


Andalusia  ... 














Bressane     ... 







Coucou  de  Rennes 














Dorking      ... 







Faverolles  ... 














La  Fleche  ... 























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246  THE   UNFERTILISED   EGG  AS  A  [pt.  iii 

again.  Malcolm  maintained  in  1902  that,  although  there  were  un- 
doubtedly differences  between  the  eggs  of  different  breeds  of  hen, 
they  did  not  exceed  the  amount  of  variation  between  individual  eggs 
from  hens  of  the  same  breed.  His  results  are  shown  in  Table  3. 
Thus,  although  the  feeding  was  carefully  controlled,  the  eggs 
from  one  hen  might  show  a  difference  of  i'i4gm.  of  fat,  while 
between  two  eggs  from  different  breeds  the  difference  might  be  only 
0-13  gm.  His  conclusions  were  supported  in  the  main  by  Carpiaux; 
Leveque  &  Ponscarme ;  von  Czadek ;  Iljin ;  and  Willard,  Shaw, 
Hartzell  &  Hole;  who  made  very  long  studies  of  a  considerable 
number  of  breeds.  Some  of  the  figures  obtained  by  von  Czadek 
and  Iljin  are  given  in  Table  5.  Von  Czadek  studied  the  Sulmtal, 
Minorca,  Orpington,  Rhode  Island,  Faverolle,  and  Wyandotte 
races,  together  with  an  Italian  and  a  Rhineland  breed.  His  outside 
values  for  egg  weight,  for  instance,  were  43  gm.  and  75  gm. — 
a  considerable  difference — but  the  former  was  from  the  Rhineland 
hen  and  the  latter  from  the  Minorca  variety.  The  span  showed  great 
variations,  thus  an  egg  weighing  55  gm.  might  be  a  heavy  Orpington 
or  a  rather  light  Faverolle  or  a  medium  weight  Italian.  The  only 
breed  which  stood  well  out  of  the  range  of  individual  differences  was 
the  Minorcas  which  laid  very  heavy  eggs.  Certain  instances  have 
shown,  however,  that  remarkable  agreement  may  exist  between  work 
done  on  eggs  of  widely  different  breeds.  Thus  the  classical  work  of 
Plimmer  &  Scott  on  the  phosphorus  metabolism  of  the  developing 
chick  was  confirmed  very  strikingly  by  Masai  &  Fukutomi,  who 
worked  in  Japan.  Here  the  correspondence  was  almost  numerical. 
But  on  the  other  hand  there  is  evidence  that  eggs  of  different  breeds 
differ  not  only  in  their  gross  characteristics,  but  also  as  regards  more 
subtle  properties;  thus  Moran  has  demonstrated  that  eggs  from 
different  breeds  of  hen  vary  very  greatly  in  their  resistance  to  cold, 
so  that  the  viability  is  different,  and  Needham,  working  on  the  inositol 
metabolism  of  the  embryo,  observed  differences  between  the  embryos 
from  Black  and  White  Leghorn  hens.  Physico-chemical  differences 
between  breeds  of  silkworm  eggs  are  enumerated  by  Pigorini. 

The  individual  differences  between  eggs  may  be  equally  important. 
Benjamin  has  shown  that  there  are  numerous  variable  factors  which 
modify  the  constitution  of  the  egg.  The  amount  of  yolk,  egg-white, 
and  water,  as  well  as  the  thickness  of  the  shell,  vary  according  to 
the  season,  diet,  age  (Riddle)  and  general  condition  of  the  bird 


in  question.  Nor  are  such  comparatively  slowly  changing  factors 
the  only  ones  which  bring  about  differences  between  individual 
eggs ;  the  time  the  egg  takes  to  pass  down  the  oviduct,  for  instance, 
will  materially  affect  the  amount  of  albumen  it  contains,  and 
such  variable  quantities  as  the  blood-sugar  level  (Riddle)  and  the 
level  of  cholesterinaemia  in  the  parent  animal  will  exercise  their 
effects  upon  the  resulting  egg.  Again,  the  length  of  time  elapsing 
between  the  laying  of  the  egg  and  the  beginning  of  incubation  will 
have  a  marked  efTect,  for  a  certain  amount  of  water  will  evaporate 
from  the  egg-contents  through  the  shell,  and  just  how  much  does  so 
will  depend  on  the  humidity  of  the  surrounding  atmosphere.  The 
process  of  water-absorption  by  the  yolk  (Greenlee)  from  the  white 
will  also  be  affected  by  these  conditions,  so  that  the  embryo  at 
the  initiation  of  its  incubatory  development  may  find  a  remarkably 
inconstant  set  of  circumstances  in  its  immediate  environment.  More- 
over, a  certain  amount  of  development  always  takes  place  in  the  egg 
after  fertilisation  as  it  passes  down  the  oviduct,  so  that  the  embryo 
has  already  gastrulated  by  the  time  that  the  egg  is  laid  by  the  hen. 
It  was  the  ignorance  of  these  facts  which  led  Malpighi,  as  we  have 
already  seen,  to  his  erroneous  conclusions,  for  if  he  had  known  of 
the  phenomenon  of  "body-heating",  as  it  is  called  by  the  poultry- 
farmer,  he  would  not  have  put  forward  the  preformation-theory,  and 
the  eighteenth  century  would  have  been  spared  the  trouble  of  getting 
rid  of  that  embryological  phlogiston.  Thus  no  two  eggs  are  ever 
exactly  the  same  age,  and  as  there  is  reason  to  believe  that  enzymic 
action  begins  in  the  yolk,  if  not  in  the  white,  very  shortly  after 
fertilisation,  this  fact  makes  it  additionally  difficult  to  get  precise  figures 
for  the  constitution  of  the  unincubated  egg.  Then  the  position  of  the 
egg  in  the  clutch  (whether  first  or  second)  in  pigeons  may,  according 
to  Riddle,  make  a  difference  of  9-15  per  cent,  in  yolk  weight.  It 
may  be  concluded  that  nothing  short  of  the  greatest  caution  must 
be  employed  in  the  material  which  is  used  for  chemico-embryological 
researches  on  the  hen's  egg.  The  individual  hens  should  be  marked, 
and  the  eggs  produced  by  them  should  be  noted,  their  food  should 
be  constant  in  composition  and  the  breed  used  should  be  not  only 
single  in  any  one  series  of  experiments,  but  also,  if  possible,  genetically 
pure.  It  is  very  greatly  to  be  wished  that  standard  hens  could  be 
obtained,  such  as  the  standard  rats  necessary  for  feeding  experiments, 
and  much  further  work,  with  a  proper  statistical  backing,  is  needed 

248  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

on  the  range  of  individual  and  racial  variations  in  all  the  properties 

of  eggs. 

The  effect  of  the  diet  of  the  hen  on  the  chemical  composition  of 

the  egg  has  been  studied  by  various  workers,  notably  by  Terroine 

&  Belin.   Except  in  certain  respects,  it  showed  a  remarkable  fixity 

of  composition : 

Table  6. 

Ordinary    Corn  and  potato     Hemp  seed 
mixed  ration  almost  ration 

ration  free  from  fats  (fatty) 

White  in  %  of  total  weight        ...  56-7  54-3                          — 

Yolk  in  %  of  total  weight          ...  31-3  34-0  33-2 

Shell  in  %  of  total  weight          ...  11-4  lo-g                          — 

Water  %           87-8  87-4  87-4 

Ash% 0-49                    —                         — 


Water  %           49-9  50-33  50-99 

Ash% 1-48                    —                         — 

Total  nitrogen  %         ...          ...  2-67                    —                         — 

Total  fatty  acids  %     28-4  26-6  2655 

Unsaponifiable  fraction  %     ...  1-85                    —  2-08 

Cholesterol  % i-i8                   1-58                      i-ii 

Lecithin  P  % —                      0-425  0-434 

Thus,  although  the  character  of  the  substances  stored  for  the  use 
of  the  embryo  can  be  varied  considerably,  as  will  be  seen  later,  the 
balance  of  them  cannot.  But  the  question  is  probably  rather  com- 
plicated, for  it  has  been  shown  by  Dam  that  by  feeding  hens  on  a 
ration  rich  in  cholesterol,  the  cholesterol  content  of  eggs  can  be  in- 
creased from  501  to  615  mgm.  per  cent,  of  the  wet  weight  or  roughly 
by  22  per  cent,  of  the  original  value.  In  another  instance  the 
cholesterol  rose  from  476  to  560  mgm.  per  cent.  This  would  not  be 
in  disagreement  with  Terroine  &  Belin's  figures,  but  it  would  be 
a  very  desirable  thing  to  make  a  detailed  study  of  the  limits  of 
variation  of  all  the  constituents  of  the  egg,  and  to  find  out  exactly 
how  different  in  chemical  composition  an  egg  can  be  from  the  normal 
while  retaining  its  hatchability.  Klein  regards  the  cholesterol  output 
of  the  hen  in  its  eggs  as  showing  a  synthesis  of  that  substance  in  the 
parent  body.  Leveque  &  Ponscarme  have  stated  that  it  was  not 
possible  to  show  any  effect  on  the  eggs  in  eleven  breeds  of  hen  by 
minor  variations  in  the  diet;  and  this  was  amply  confirmed  by  Gross. 

The  ingenious  and  partially  successful  attempt  of  Riddle  and 
Behre  &  Riddle  to  make  hens  preserve  their  own  eggs  by  feeding 
them  with  hexamethylenetetramine,  sodium  benzoate,  and  sodium 


salicylate,  may  here  be  mentioned.  Starting  out  from  this  practical 
suggestion  the  work  led  to  the  discovery  of  a  number  of  specific 
effects  of  substances  such  as  quinine  on  egg  size  and  yolk  size.  Thus 
Riddle  &  Basset  found  that  alcohol  markedly  reduces  yolk  size  in 
pigeons,  Riddle  &  Anderson  found  that  quinine  reduces  egg  size, 
yolk  size  and  albumen  size  but  has  no  effect  on  the  protein/fat  ratio 
of  the  egg,  while  Behre  &  Riddle  found  that  the  diminution  of 
albumen  size  under  quinine  bore  more  on  the  solids  than  on  the 
water  and  involved  considerable  reduction  of  the  protein. 

The  elaborate  investigations  on  the  egg  of  the  tern,  already 
mentioned,  led  to  a  significant  correlation  between  abundance  of 
food  and  size  of  egg,  and  it  is  certain  that  the  size  of  the  hen's  egg  is 
affected  by  its  diet  since  the  work  of  Atwood.  There  seems  also  to  be 
a  seasonal  fluctuation,  the  weight  of  the  eggs  increasing  from  July 
to  February  and  decreasing  from  March  to  June.  These  seasonal 
fluctuations  appeared  distinctly  in  Atwood's  data,  and  explain  the 
results  of  Curtis  and  of  Fere.  Rice,  Nixon  &  Rogers  and  Riddle 
found  a  definite  relation  between  the  amount  of  food  consumed  and 
the  number  of  eggs  produced,  both  of  these  factors  varying  exactly  with 
the  seasonal  variation  in  the  egg  size.  Fluctuations  of  a  regular  kind 
seem  even  to  occur  each  month,  according  to  Hadley  who  observed 
such  changes  in  egg  weight  and  number.  According  to  Curtis  the  size 
of  the  eggs  increases  as  the  laying  bird  matures,  in  the  case  of  the  hen, 
and  Pearson  has  observed  similar  variations  in  the  case  of  the  sparrow. 

The  genetics  of  egg  production  have  been  studied  by  Pearl  and 

The  relation  between  the  egg  weight  and  the  chick  weight  at 
hatching  has  been  studied  by  Halbersleben  &  Mussehl  and  by 
Iljin.  The  former  workers  found  a  quite  consistent  relation  within 
one  breed  between  the  weight  of  the  egg  before  incubation  and  the 
weight  of  the  chick  at  hatching,  the  latter  averaged  64  per  cent,  of 
the  former.  After  thirty-five  days  of  post-natal  life,  however,  the 
slight  advantage  possessed  by  the  chicks  from  the  heavier  eggs  had 
altogether  disappeared.  They  also  noted  that,  other  things  being  equal, 
chicks  hatched  from  the  more  pigmented  eggs  (browner)  weighed 
slightly  more  than  those  hatched  from  the  less  pigmented  ones. 
Abnormally  large  and  abnormally  small  eggs  did  not  hatch  as  well 
as  those  of  medium  weight.  Iljin  collected  a  great  many  figures  but 
his  text  contains  no  statistical  analysis. 

250  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

Stewart  &  Atwood  reported  that  chicks  hatched  from  pullet  eggs 
were  neither  so  large  nor  so  vigorous  as  those  hatched  from  the  eggs 
of  hens  two  or  three  years  old.  Whether  there  is  here  a  direct  effect 
on  the  chick  of  the  age  of  the  hen,  or  whether  the  effect  is  indirect, 
due  to  the  small  size  of  the  egg,  may  be  well  questioned. 

What  relations  exist  between  the  chemical  constitution  of  the  egg 
and  the  percentage  "hatchability"  are  at  present  obscure,  owing 
perhaps  to  the  comparative  crudity  of  our  estimation  methods.  The 
work  of  Pearl  &  Surface  indicated  definitely  that  differences  in  the 
hatchability  of  eggs  are  determined  by  or  associated  with  innate 
differences  in  the  individual  hens  which  laid  them,  that  these  dif- 
ferences are  probably  inherited,  and  that  variations  within  rather 
wide  limits  in  certain  environmental  factors,  e.g.  the  temperature, 
during  incubation,  are  of  secondary  importance  in  determining  the 
death  or  the  hatching  of  the  embryo.  Hatchability  of  embryos  would 
appear  then  to  be,  like  fecundity,  a  heritable  character.  The  experi- 
ments of  Lamson  &  Card  confirmed  the  conclusions  of  Pearl  & 
Surface,  but  although  some  physico-chemical  mechanism  is  un- 
doubtedly at  work,  these  statistical  studies  gave  no  hint  as  to  its 

Dunn  determined  to  probe  further  into  it.  In  his  first  paper  he 
argued  that  if  hatchability  was  associated  with  constitutional  vigour, 
it  should  show  a  correlation  with  such  a  value  as  the  chick  mortality 
in  the  first  three  weeks  of  post-natal  life.  Experimentally  this  was 
not  the  case,  e.g.  post-natal  mortality  remained  the  same,  although 
in  two  instances  the  pre-natal  mortality  was  on  the  one  hand  ex- 
tremely high  (20-39  per  cent,  hatchability)  and  on  the  other  hand 
extremely  low  (80-100  per  cent,  hatchability).  It  therefore  seemed 
likely  that  mortality  before  and  after  hatching  is  determined  by  quite 
different  factors.  The  more  specific  influences  operating  in  embryonic 
life  must  doubtless  be  looked  for  in  the  physico-chemical  constitution 
of  the  unincubated  egg. 

Hays  &  Sumbardo,  in  a  search  for  such  influences,  were  able  to 
exclude  statistically  fresh  weight,  length,  diameter,  specific  gravity, 
shell  thickness,  outer  and  inner  shell-membrane  thickness,  porosity 
and  imbibition  of  water  from  25  per  cent,  salt  solution.  Other  factors 
which  have  been  excluded  are  percentage  of  protein  in  the  diet  of 
the  laying  hen  (Rosedale),  percentage  of  yolk-pigment  (Benjamin), 
evaporation  rate  of  the  egg  (Dunn),  yolk-fat  percentage  (Cross),  egg- 


fat  percentage  (Cross),  yolk-protein  percentage  (Cross),  egg-protein 
percentage  (Cross),  egg-phosphorus  percentage  (Cross),  chick- 
phosphorus  percentage  (Cross). 

It  appears,  however,  that  the  constitution  of  the  egg-proteins  may- 
be influenced  by  the  presence  of  unusual  proteins  in  the  diet  of  the 
hen,  and  that  this  may  influence  hatchability.  Pollard  &  Carr  have 
reported  the  results  of  feeding  the  following  proteins  to  laying  hens : 
wheat,  rye,  corn,  oats;  kaffir,  barley,  peas,  soya,  hemp;  buckwheat, 
popcorn,  sunflower  seed. 

The  first  group  of  four  (all,  of  course,  being  fed  alone)  were  very 
efficient  for  the  production  of  normal  eggs;  the  second  group  (of 
five)  permitted  the  hens  to  lay  eggs  but  the  eggs  were  hardly  hatch- 
able  at  all,  while  the  third  group  allowed  of  no  eggs.  Pollard  & 
Carr  studied  the  egg-proteins  in  all  cases  and  obtained  evidence  of 
tryptophane  deficiency  in  the  second  group,  so  that  they  concluded 
that  a  minimum  tryptophane  content  was  essential  for  successful 
development  through  hatching.  It  is  unfortunate  that  their  results 
were  never  published  in  full. 

The  effect  of  sex  on  the  chemical  composition  of  the  egg  has  been 
discussed  by  Riddle.  As  is  well  known,  in  some,  probably  most, 
animals,  the  male  produces  two  kinds  of  spermatozoa  which  are  not 
equal  in  their  prospective  sex  value,  i.e.  some  which  will  give  rise 
to  females  and  some  which  will  give  rise  to  males.  In  birds,  on  the 
other  hand,  the  dimorphism  of  the  germs  exists  not  in  the  spermatozoa 
but  in  the  egg-cells.  The  female  produces  two  kinds  of  eggs  of  unequal 
prospective  sex  value.  Riddle  found  that  pure  wild  species  of  doves 
and  pigeons  were  ideal  material  for  studies  on  sex,  since  very  abnormal 
sex-ratios  could  easily  be  obtained  from  them,  and  his  studies  led 
him  to  the  view  that  sex  was  more  a  matter  of  metabolic  level  or 
rate  of  protoplasmic  activity  than  anything  else.  But  what  concerns 
us  here  are  the  consistent  differences  which  he  was  able  to  demon- 
strate between  male  and  female  eggs. 

Pigeons  generically  crossed,  when  not  permitted  to  lay  many  eggs, 
produce  only  males,  but  when  made  to  lay  many  eggs  produce  first  only 
males,  and  eventually  "under  stress  of  overwork"  only  females.  These 
facts  and  their  proper  conditions  having  been  ascertained  previously 
by  extensive  statistical  investigations,  the  way  lay  open  for  the 
chemical  analysis  of  the  two  sorts  of  pigeon's  eggs.  900  analyses 
were  made  and  more  than  12,000  yolks  weighed. 



[PT.  Ill 

Fig.  14,  taken  from  Riddle,  gives  the  differences  diagrammatically. 
A  glance  at  it  shows  that  the  male-producing  egg  of  the  spring 
contains  less  stored  material  than  the  female-producing  egg  of  the 

Sex  conbrol  and   known    correlations  in  pigeons 



d     cf     cT     d*     cT     ^      $    ^^    *?    *$    ^9    •.>'    ^ •-':      "■ 

9       10       11     12    13      14 

N?    1 

N°    <2 

N°   3 

N9   4 

N?  5 

N°  6 

N?   7 

N9  8 

N°  9 



N0I.  shows    comparabive    size   of  eggs  of  Alba  (A) 
and    Orienbalis  (0) 

Fig.  14. 

autumn.  The  amount  of  water  and  ash  present,  on  the  other  hand, 
diminishes,  and  the  rise  indeed  is  mainly  to  be  seen  in  the  fat  and 
lipoid  fractions  and  in  the  calorific  value.  Table  7  gives  the  figures 
for  one  individual  pigeon   during    191 2.    The  differences   are   not 

SECT.    l] 



large,  but  they  were  invariably  found.  Another  series  of  figures  show- 
ing the  rise  in  calorific  value  during  the  course  of  the  year  and  the 
transition  fi-om  male  to  female  eggs  is  given  in  Table  8.  Here  also 
the  increase  is  unmistakable.  Within  one  clutch,  also,  the  water- 
content  of  the  second  egg  is  lower  and  the  calorific  value  higher  than 
the  first  egg,  which  fits  in  very  well  with  the  fact  that  under  normal 


May  26 


June     7 



July     3 











Table  7.   Effect  of  sex  on  pigeon's  eggs. 

Female  Turtur  orientalis  x  Streptopelia  alba,  no.  410  for  191 2. 

%  wet  weight  %  dry 

Analysed  Weight     t ^ ^      weight 

or  in-         of                      Pro-    Extrac-                             ale-  Calories 

cubated     yolk      Lipoid     tein       tives       Ash    Water      sol.  per  egg  Sex 

An.        2-330      18-32     25-44      5-28      4-85     5701     72-65  7405  — 

An.        2-660      17-54     25-63      5-25       2-62     54-82     72-45  8990  — 

Inc.          —           —          —          —          —         —          —  —  Male 

Inc.          —           —          —          —          —         —          —  —  Male 

Inc.          —           —          —          —          —         —          —  —  Male 

An.        2-026      16-49     26-00      3-63       2-43     56-05     71-95  6714  — 

An.        2-330      19-18     26-55      3-75       1-93     5522     72-27  7881  — 

Inc.          —           —          —          —          —         —          —  —  Male 

Inc.          —           —          _____  _  Male 

An.        2-422      17-82     25-88      3-82       I -80     55-84     72-42  8061  — 

An.        2-720      18-88     25-96      3-86       1-81     55-33     72-45  9296  — 

Inc.          _______  _  Male 

Inc.          —           —          —          —          —         —          —  —  Male 

Inc.          —           —          —          —          —         —          —  —  Male 

Inc.          —           —          —          —          —         —          —  —  Female 

Inc.          —           —          —          —          —         —          —  —  Female 

Inc.          —           —          —          —          —         —          —  —  Female 

An.        2-700      21-40       —          —          —      55-45     73-17  9323  — 

An.        2-715      21-63        —          —          —      55-39     73-02  9383  — 

Table  8.   Eggs  from  the  same  female  Streptopelia  risoria  (1914). 


Weight  of  yolk      Energy  in  cals. 

June  6 










I -000 


July  14 






Aug.  30 



Nov.  6 












Dec.   I 


















254  THE   UNFERTILISED   EGG  AS    A  [pt.  iii 

conditions  the  first  egg  laid  nearly  always  gives  rise  to  a  male  and  the 
second  to  a  female. 

In  Fig.  14  the  line  marked  "developmental  energy"  implies  that 
a  higher  percentage  of  the  male  eggs  hatch  successfully  than  of  the 
female  eggs.  The  data  for  length  of  life  show  the  same  curve.  The 
smaller  eggs  of  both  clutch  and  season  are  the  eggs  which  give 
positive  results  in  strength  and  vigour  tests,  and  the  larger  eggs  are 
those  which  are  liable  to  display  weakness.  These  facts  are  in  entire 
accord  with  the  higher  metabolic  level  which  Riddle  associates  with 
the  small  male  eggs.  It  is  interesting  to  note  that  Lawrence  & 
Riddle  found  consistently  higher  values  for  total  fat  and  total  phos- 
phorus in  the  blood  of  female  fowls  than  in  that  of  male  fowls,  from 
which  they  concluded  that  the  metabolic  differences  between  male 
and  female  germs  persist  in  the  adult,  and  all  these  facts  are  in  agree- 
ment with  the  work  of  Goerttler  and  Baker  on  human  and  Smith  on 
crustacean  blood-fat,  and  of  Benedict  &  Emmes  on  sex  differences 
in  basal  metabolism.  But  for  further  discussion  of  the  metabolic 
theory  of  sex,  the  papers  of  Riddle  must  be  consulted.  Interesting 
data  on  the  hatchability,  vigour,  etc.,  of  rotifer  eggs  are  contained 
in  the  paper  of  Jennings  &  Lynch,  but  these  authors  made  no 
chemical  experiments. 

To  say,  as  Riddle  does,  that  there  are,  as  it  were,  two  kinds  of  eggs 
in  some  species,  one  male-producing,  and  the  other  female-producing, 
may  either  be  taken  to  mean  that  there  are  quantitative  differences 
between  them  or  that  their  constituent  substances  are  qualitatively 
chemically  different,  or,  thirdly,  that  the  same  substances  in  the  same 
quantities  are  differently  distributed  spatially  and  temporally.  As  will 
be  seen  later  in  connection  with  the  lipoids  of  mammalian  egg-cells, 
the  second  view  finds  supporters,  and  some  such  opinion  is  held 
by  Russo.  Faure-Fremiet,  in  the  course  of  his  work  on  the  egg  of 
Ascaris  megalocephala,  to  which  he  applied  every  conceivable  method, 
examined  a  very  large  number  of  individual  eggs  in  order  to  find 
whether  they  separated  at  all  chemically  into  two  types.  His  method 
was  to  centrifuge  them  separately,  much  as  McClendon  had  done 
with  the  frog's  egg,  and  then  to  measure  in  mm.  the  thickness  of 
{a)  the  mitochondria  layer,  and  {b)  the  fatty  layer.  Fig.  15  {a)  taken 
from  his  paper  shows  the  frequency  polygon  which  he  constructed 
on  the  basis  of  these  results,  the  ordinate  giving  the  number  of  eggs 
measured,  and  the  abscissa  the  thickness  of  the  mitochondrial  layer. 

SECT.    l] 



It  is  quite  evident  that  there  are  not  two  modes  on  the  line  joining 
the  points,  i.e.  that  there  are  not  two  types  of  eggs,  but  only  one  type. 
Faure-Fremiet  made  very  similar  experiments,  determining  the  gly- 
cogen content  of  the  eggs  histo-colorimetrically  with  iodine  solutions, 
and  there  also  the  frequency  polygon  had  but  one  mode  (Fig.  15  (^)). 
But  this  second  case  was  based  on  an  unsatisfactory  method.  In  the 
particular  instance  under  investigation,  neither  mitochondria  nor 



12     3^5 




J : 

<k  5  0  7  8 

Fig.  15- 

glycogen  happens  to  be  an  entity  which  varies  as  between  the  two 
kinds  of  eggs.  Nevertheless,  the  plan  of  work  was  an  interesting  one, 
and  widely  extended  researches  with  it,  using  accurate  chemical 
methods,  would  be  very  desirable. 

1-5.    The  Shell  of  the  Avian  Egg 

Litde  attention  has  been  paid  to  the  shell  of  the  bird's  egg  from  a 
physiological  point  of  view.  The  relevant  analyses  are  given  in 
Table  9.  There  is  some  difference  between  the  shells  of  different 








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SECT.   l] 



birds,  and  it  would  be  interesting,  for  example,  to  know  why  the 
pheasant's  contains  such  an  unusually  high  percentage,  of  phos- 
phorus, and  why  the  herring  gull's  has  so  high  a  percentage  of  organic 
substance.  A  certain  interest  attaches  to  the  determinations  of 
Balland  on  ostrich  eggs,  some  from  a  tomb 
of  the  Hellenistic  period  and  others  from 
modern  ostriches,  but  the  differences  he 
found  were  probably  not  very  significant, 
as  the  analysis  of  Torrance  seems  to  give 
values  half-way  between  those  of  Balland. 
Neither  Balland,  Torrance  nor  Wicke  states 
whether  the  ostrich  used  was  the  North 
or  South  African  variety,  a  complication 
which  might  make  a  difference.  Wicke 
believed  that  the  difference  in  shell-com- 
position between  different  kinds  of  birds 
was  almost  entirely  dependent  on  their 
usual  foods. 

The  microscopic  structure  of  the  shell 
was  investigated  by  Nathusius  in  the  'sixties, 
and  since  then  little  has  been  added  to  his 
work.  The  shell  consists  of  an  outer  layer  of 
crystals  of  calcium  carbonate  arranged  with 
their  long  axes  perpendicular  to  the  bound- 
ing surface  (Fig.  16),  and  an  inner  layer 
composed  of  undifferentiated  calcium  car- 
bonate (Herzog  &  Gonell).  Kelly;  Schmidt; 
Meigen  and  Osawa  have  found  that  the 
mineralogical  form  of  the  lime  is  invariably 
calcite,  no  aragonite  being  present  in  any 
bird's  egg-shell.  This  has  been  confirmed 
with  X-ray  analysis  by  Mayneord.  The 
ostrich,  Emj>s  europaea,  is  the  only  doubtful  case,  for  Kelly  identified 
its  egg-shell  lime  as  conchite,  but  Torrance  considers  it  to  be  calcite. 
Prenant's  review  should  be  consulted  for  further  details  regarding 
this  interesting  biochemical  problem.  Only  one  paper  exists  dealing 
with  the  changes  which  the  shell  undergoes  histologically  during  the 
development  of  the  chick;  it  will  be  considered  in  the  section  on  em- 
bryonic respiration,  where  the  data  we  possess  on  the  question  of  the 
NEi  17 

-^:- -;>.,«■  j 

Fig.  16.  a,  Outer  crystalline 
layer;  b,  c,  d,  amorphous 
layers;  e,  mamillae;  /,  shell- 



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26o  THE   UNFERTILISED   EGG  [pt.  m 

permeability  of  the  shell  and  its  membranes  will  also  be  dealt  with. 
There  has  been  some  controversy  on  the  subject  of  whether  the  egg- 
shell contains  any  elements  of  the  secreting  organ  in  it,  like  the  decidua 
of  mammals.  Von  Baer  thought  not,  but  the  presence  of  cellular 
structures  has  been  reported  by  von  Hemsbach;  Landois;  and 

The  shell-membrane  has  been  studied  chemically  by  Liebermann 
and  Lindwall,  who  found  that  it  consisted  almost  entirely  of  a  protein, 
the  percentage  composition  of  which  agreed  very  closely  with  keratin 
(Table  loa).  Krukenberg,  alone,  on  the  ground  of  its  reactions,  held 
it  to  be  a  mucin.  This  ovokeratin,  which  contains  four  times  as  much 
sulphur  as  the  albumen  of  the  egg-white,  was  found  by  Morner  to 
include  7  per  cent,  of  cystine,  but  there  are  reasons  for  supposing 
that  this  figure  is  much  too  low.  Nothing  is  known  of  the  part 
played  by  ovokeratin  in  embryonic  metabolism,  but,  in  view  of  the 
fact  that  calcium  is  transported  from  the  shell  to  the  embryo  during 
the  period  of  ossification  of  embryonic  cartilage,  it  is  not  impossible 
that  the  sulphur  or  the  cystine  of  ovokeratin  may  be  made  use  of 
in  a  similar  manner  to  meet  the  need  for  sulphur  and  cystine 
for  the  feathers.  This  will  be  discussed  later  under  the  head  of 
sulphur  metabolism  (Section  I2'7).  Morner  considered  that  sulphur 
must  exist  in  the  ovokeratin  in  other  forms  besides  cystine,  for  that 
amino-acid  would  not  account  for  more  than  a  third  of  what  he  found 
was  there.  The  amino-acid  analyses  of  ovokeratin  are  placed  in 
Table  1 1 ;  they  are  due  to  Abderhalden  &  Ebstein,  and  to  Plimmer  & 
Rosedale,  the  former  by  isolation  and  the  latter  by  the  van  Slyke 
nitrogen  distribution  method.  The  arginine  figure  is  rather  high. 

The  strength  of  the  shell  is  clearly  an  important  biological  factor : 
according  to  Romanov  its  average  thickness  is  0*3 11  mm.  giving  a 
breaking-strength  of  4-46  kilos.  The  relation  between  shell-thickness 
and  breaking-strength  is  a  straight  line. 

The  physiological  properties  of  the  shell  of  the  bird's  egg  have  been 
very  insufficiently  studied.  In  the  last  century  there  was  a  general 
impression  that  the  shell  possessed  a  differential  permeability  and 
that,  while  water  and  other  liquids  would  readily  go  through  the 
egg-shell  and  its  membranes  from  outside  in,  they  would  not  easily 
pass  from  the  inside  to  the  outside.  It  is  difficult  to  find  how  this 
idea  originated;  thus  Ranke  in  1872  attributed  it  to  the  younger 
Meckel,  and  Ranke's  own  statement  was  subsequently  copied  down 


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264  THE   UNFERTILISED   EGG   AS   A  [pt.  hi 

wrongly  by  Schafer.  However,  Thunberg  in  1902  conclusively 
demonstrated  the  error  of  the  belief,  and  showed  experimentally 
that  water  would  pass  through  the  membranes  equally  well  both  ways, 
though  he  found  that  of  the  two  the  inner  one  was  the  less  permeable. 
In  the  case  of  water  birds,  there  is  evidence  that  the  shell  is  absolutely 
impermeable  to  water;  Loisel,  for  instance,  found  that  the  eggs  of 
the  grebe,  Podiceps  cristatus,  and  the  duck,  Anas  domesticus,  when 
placed  in  distilled  water  absorbed  not  a  trace  of  it,  and  gave  out 
no  chloride  to  it  over  a  period  of  many  hours.  The  eggs  of  the 
ordinary  hen,  on  the  other  hand,  increased  considerably  in  weight 
and  allowed  some  chloride  to  pass  out  into  the  water.  At  the  same 
time,  Loisel  found  that  hen's  eggs  develop  quite  normally,  at  any 
rate  up  to  the  seventh  day,  even  if  they  are  lying  in  water.  This 
experiment  of  Loisel's  was  confirmed  by  Lippincott  &  de  Puy,  who 
succeeded  in  hatching  chicks  from  eggs  incubated  while  lying  in  |  in. 
of  distilled  water.  The  differences  between  these  eggs  and  the  controls 
suggested  that  the  eggs  lying  in  the  water  not  only  failed  to  lose  as 
much  water  through  evaporation  as  eggs  incubated  under  ordinary 
conditions,  because  of  the  limitation  of  the  evaporating  surface, 
but  actually  absorbed  some  water.  Trials  with  rhodamine  red  and 
methylene  blue  demonstrated  penetration  by  these  dyes,  extending  in 
the  former  case  to  vital  staining  of  the  embryo.  It  is  known  (Rizzo) 
that  the  avian  egg-shell  has  many  pores  (o-86  to  1-44,  average  1-23 
per  sq.  mm.). 

As  regards  gases,  the  only  paper  is  that  of  Hiifner.  Hiifner  placed 
small  pieces  of  egg-shell  with  their  membranes  in  a  diffusiometer, 
and  measured  the  rate  at  which  gases  passed  through  the  obstacle. 
He  found  that  oxygen  diffused  through  with  most  difficulty,  then 
nitrogen,  then  carbon  dioxide,  and,  finally,  hydrogen  most  easily. 
It  may  be  significant  that  carbon  dioxide  would  thus  appear  to  be 
able  to  escape  somewhat  quicker  than  oxygen  can  enter.  But  under 
normal  atmospheric  pressure  the  amount  diffusing  through  the  whole 
egg-shell  (goose)  per  second  was  2-115  c.c.  of  oxygen  and  0-503  c.c. 
of  carbon  dioxide.  The  diffusion  velocity  was  always  proportional 
to  the  partial  pressure  of  the  gases,  and  the  removal  of  the  inner 
membrane  made  no  difference  at  all,  suggesting  that  the  principal 
barrier  was  the  amorphous  calcium  carbonate  layer.  It  would 
be  very  desirable  to  repeat  these  observations  with  more  modern 
methods,  and  on  a  greater  variety  of  eggs. 


1-6.    The  Avian  Egg-white 

The  white  of  the  egg  is  divisible  into  three  portions  which  have 
been  studied  separately  by  Romanov.  The  outermost  and  thinnest 
layer  makes  up  39-8  %  of  the  whole  and  has  1 1'6  %  dry  solid.  The 
middle  layer  accounts  for  57-2  %  and  has  12-4%  dry  solid,  and  the 
innermost,  thickest,  layer  is  only  3  %  and  has  i4'5  %  dry  solid*.  The 
chalazae  have  only  once  been  analysed  separately  (Liebermann), 
when  the  elementary  composition  of  their  protein  was  ascertained. 
Table  1 2  summarises  the  results  of  the  investigators  who  have  made 
general  analyses  of  the  white.  It  is  a  very  watery  solution  of 
protein,  containing  only  the  most  negligible  traces  of  fats  and 
lipoids,  but  a  great  many  water-soluble  substances  such  as  carbo- 
hydrate in  various  forms,  protein  breakdown-products,  choline, 
inositol,  etc.  Natural  egg-white,  according  to  Rakusin  &  Flieher, 
is  a  saturated  solution  of  ovoalbumen  (15-35  P^^  cent.).  The 
water-content  does  not  vary  much,  but  Tarchanov's  analyses  go 
to  show  that  the  smaller  eggs  with  short  incubation-time  are 
wetter  than  the  others.  The  proteins  of  the  egg-white  are  believed 
to  be  variable  in  number  in  the  eggs  of  different  birds.  In  that 
of  the  hen,  four  are  known,  in  that  of  the  crow  three,  and  in  that 
of  the  dove  one  only.  The  egg-white  of  the  hen's  egg  contains  two 
albumens,  ovoalbumen  and  conalbumen,  and  two  glucoproteins, 
ovomucoid  and  ovomucin. 

It  was  at  one  time  thought  that  there  was  a  fifth,  ovoglobulin. 
Dillner  studied  it  in  1885,  and  estimated  that  it  made  up  0-67  per 
cent,  of  the  egg-white  and  6-4  per  cent,  of  the  total  protein,  but 
Osborne  &  Campbell  showed  that  it  was  simply  a  mixture  of  the 
others  in  different  proportions.  This  had  already  been  made  probable 
by  the  results  obtained  by  Corin  &  Berard,  who  were  able  to  separate 
the  ovoglobulin  into  two  or  three  constituent  proteins  having 
several  different  coagulation  temperatures  (57*5°,  67°,  72°,  76°  and 
82°  C.)  and  other  special  characteristics. 

Hofmeister  was  the  first  to  prepare  crystalline  ovoalbumen,  and 
he  published  several  papers  on  it.  Other  workers  confirmed  his  dis- 
covery, such  as  Gabriel ;  Harnack ;  and  Bondzynski  &  Zoja,  but 
Hopkins  &  Pincus  showed  that  the  albumen  so  crystallised  only 
accounted  for  half  the  protein  present  in  the  egg-white.  Part  of  the 
missing  protein  was  found  by  Osborne  &  Campbell  to  be  in  the 

*  A  large  number  of  concentric  rings  can  be  seen  in  egg-white  coagulated  in  situ, 
according  to  Remotti. 



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268  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

Table  13.   Distribution  of  proteins  in  avian  egg-white 




Passeres  (singing  birds) 
Turdus  iliacus 
Turdus  piliaris    ... 
Anthus pratensis  ... 
Anthus  cervinus    ... 
Garrulm  infaustus 
Corvus  cornix 
Corvus  nionedula  ... 

Zygodactyli  (2-toed) 
Dryocopus  martins 

Accipitres  (birds  of  prey) 
Strix  aluco 
Falco  gyrfalco 
Falco  peregrinus  ... 
Falco  aesalon 
Falco  tinnunculus... 
Astur  palumbariiis 
Buteo  lagopus 
Pandion  haliaetiiis 

Pullastrae  (doves) 
Columba  livia 

Gallinae  (fowls) 
Gallus  domesticus 
Meleagris  gallopavo 

Grallae  (marsh  birds) 
Charadrius  apricarius 
Haematopus  ostralegus 
Tringa  alpina 
Phalaropus  hyperboreus 
Totaniis  glareola  . . . 
Actitis  hypoleiicos 
Limosa  lapponica 
Numenius  arquatiis 
Numenius  phaeopus 
Fulica  atra 

Lamellirostres  (ducks) 
Anser  segetum 
Fuligula  marila   ... 
Fuligula  fuligula 
Oedemia  fusca 
Clangida  glaucion 
Somateria  mollissima 
Mergus  senator   . . . 

%  wet 


%  of  total  protein 
in  eg5-white 
















I  "49 








and  date 

Osborne  &  Campbell 

(1909),         r^ 

Komori  (1920) 
Needham  (1927) 
Morner  (19 12) 

—       Morner  (1912) 




Table  13  [cont.]. 

%  wet 


%  of  total  protein 
in  egg-white 


ovo-         ovo-         ovo- 
mucoid    mucin    albumen 

and  date 

Steganopodes  (pelicans) 
Phalawcrocorax  carbo 
Phalarocrocorax  graculus  ... 


2-o8           —             — 

Mdrner  (191 2) 

Longipennes  (swallows) 
Larus  cantis 
Lesiris  crepidata  ... 
Sterna  macrura     ... 
Sterna  hirundo 



15-00          —             — 


Pygopodes  (divers) 

Podiceps  cristatus 
Colymbus  arcticus 


—             —             — 


form  of  the  two  glucoproteins  and  the  other  albumen,  while  part  of 
it  was  accounted  for  by  the  fact  that  the  yield  of  the  crystallising 
process  is  not  great.  Ovomucoid  was  originally  discovered  by 
Neumeister,  who  called  it  "pseudopeptone",  and  first  studied  by 
Salkovski  and  Zanetti. 

The  investigations  of  Osborne  &  Campbell,  whose  memoir  is  the 
best  on  this  subject,  give  no  very  definite  indication  of  the  pro- 
portions in  which  these  proteins  make  up  the  protein  fraction  of 
egg-white,  but  they  put  ovoalbumen  at  about  80  per  cent.,  and 
ovomucin  at  about  7  (see  Table  13).  Later,  Komori  estimated  that 
ovomucoid  accounted  for  about  10-5  per  cent,  of  the  proteins,  and 
in  1927  I  obtained  a  figure  of  7-6  per  cent,  for  the  same  con- 
stituent. Morner,  in  his  extensive  study  of  ovomucoid  in  numbers 
of  birds'  eggs,  obtained  results  from  which  higher  figures  emerge  on 
calculation,  namely,  from  10  to  20  per  cent.  The  only  exceptions 
were  the  pelicans,  which  seemed  to  have  very  little  ovomucoid.  The 
most  probable  relationship  between  the  proteins  is  as  follows: 
ovoalbumen  75,  ovomucoid  15,  ovomucin  7  and  conalbumen  3  per 
cent.,  but  these  values  are  only  very  approximate,  and  further  work  on 
this  point  is  much  to  be  desired.  Leaving  out  ovomucin,  Wu  &  Ling 
found  that  the  proportions  were  as  follows  (for  Gallus  domesticus) : 
ovoalbumen  78-3,  ovomucoid  12-3  and  conalbumen  9-4  per  cent.,  or 
1-34,  0-21 1  and  o-i6i  gm.  per  cent,  respectively.  Certain  Russian 
workers  (Worms  and  Panormov)  have  described  two  proteins,  anatin 
and  anatidin,  in  the  egg-white  of  the  duck's  egg,  and  three,  corvin, 

270  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

corvinin  and  corvinidin,  in  the  egg  of  the  crow.  It  is  not  certain, 
however,  to  which  of  the  well-known  proteins  of  the  hen's  egg-white 
these  others  correspond.  Judging  from  the  percentage  composition 
tables  in  Table  lo  a,  the  columbin  of  the  dove's  egg  corresponds 
to  hen  ovoalbumen  and  to  duck  anatinin,  while  duck  anatin  corre- 
sponds to  hen  ovomucin,  but  in  the  absence  of  definite  information 
the  question  must  be  regarded  as  unsettled,  and  would  repay  further 

The  minimal  molecular  weight  of  ovoalbumen,  according  to 
Cohn,  Hendry  &  Prentiss,  is  33,800  (Marrack  &  Hewitt  suggest 
43,000),  and  its  percentage  composition  is  seen  in  Table  10 a; 
the  best  analyses  are  probably  those  of  Osborne  &  Campbell, 
who  give  an  account  of  its  general  properties.  It  has  been  further 
analysed  by  several  workers  who  have  determined  the  proportions 
of  its  constituent  amino-acids,  and  whose  results  are  seen  in 
Table  11.  The  hydrolyses  of  Osborne,  Jones  &  Leavenworth; 
Osborne  &  Gilbert,  and  of  Abderhalden  &  Pregl  were  all  done  by 
acid,  but  those  of  Hugounenq  &  Morel  and  Skraup  &  Hummel- 
berger  were  alkaline,  the  former  using  baryta.  The  figures  agree 
accordingly,  and  all  that  can  be  said  of  them  is  that  for  purposes  of 
calculation  the  amounts  of  amino-acids  must  be  taken  as  minimum 
in  each  case.  Attention  may  also  be  drawn  to  the  less  complete 
analyses  of  Chapman  &  Petrie  and  Hugounenq  &  Galimard  and  to 
the  analysis  of  mixed  egg-white  proteins  by  Plimmer  &  Rosedale, 
using  the  van  Slyke  technique.  The  large  amounts  of  hexone  4Dases 
found  by  them  contrast  with  those  found  by  the  remaining  workers, 
using  direct  isolation,  and  if  this  is  not  due  simply  to  difficulties  of 
technique  it  may  lead  us  to  expect  a  high  content  of  hexone  bases 
in  conalbumen  and  ovomucin  when  they  come  to  be  analysed. 

In  Table  10  a  the  results  obtained  by  Gupta  on  the  hydrolysis  pro- 
ducts of  ovoalbumen  are  given  (see  also  Rudd).  It  is  noticeable  in 
them,  as  in  the  analyses  of  ovoalbumen  itself,  that  they  contain 
a  high  proportion  of  sulphur,  though  not  so  much  as  ovomucoid. 
The  spontaneous  evolution  of  hydrogen  sulphide  by  egg-white 
on  standing  has  long  been  known,  and  was  made  the  subject 
of  a  paper  in  1893  by  Rubner,  Niemann  &  Stagnita,  who  found 
that  100  gm.  of  egg-white  gave  off  when  boiled  with  water  10-7  mgm. 
of  HgS.  Hausmann  later  decided  that  its  source  must  be  some  labile 
sulphydryl  grouping  in  the  ovoalbumen  molecule.    In  1922  Harris 


observed  that  raw  egg-white  was  quite  non-reactive  towards  the 
nitroprusside  test  for  sulphydryl  groups,  but  that  immediately  upon 
coagulation  by  heat  it  became  vividly  reactive,  and  gave  an  intense 
purple  colour.  This  change  only  took  place  in  conditions  where 
denaturation  of  the  protein  was  involved,  and  Harris  suggested  that 
this  treatment  might  unmask  a  thiopeptide  linkage  or  some  similar 
arrangement  which  by  hydrolysis  or  keto-enol  transformation  would 
give  rise  to  an  active  sulphydryl  group  in  the  resulting  metaprotein 
molecule.  Later,  Harris  found  that  only  14  per  cent,  of  the  sulphur 
in  ovoalbumen  could  be  accounted  for  as  cystine,  so  that  some  un- 
known sulphur  compound  must  be  present  in  considerable  quantity, 
and  an  exactly  similar  finding  was  later  reported  by  Osato  for  the 
egg-membrane  protein  of  the  herring.  The  cystine  recoverable  from 
serum  albumen,  on  the  other  hand,  accounted  for  86  per  cent,  of 
the  sulphur  there.  The  possibilities  of  these  facts  with  relation  to  the 
metabolism  of  the  embryo  have  not  yet  been  explored.  Philothion, 
according  to  de  Rey-Pailhade,  exists  in  the  egg-white  of  the  hen 
but  not  in  that  of  the  duck. 

The  principal  investigation  of  ovomucoid  is  that  of  Morner.  He 
had  previously  discovered  that  percaglobulin,  a  protein  extracted 
from  the  unripe  ovarial  fluid  of  the  perch  {Perca  fluviatilis)  would 
precipitate  ovomucoid  from  its  solution.  With  this  reagent  he  made 
an  examination  of  a  wide  variety  of  birds'  eggs,  in  order  to  study 
the  distribution  of  ovomucoid.  By  direct  estimation  he  found  it  to 
be  present  in  all  the  eggs  he  studied,  but  it  seemed  to  exist  in  two 
sharply  distinguished  forms,  one  which  would  give  a  precipitate  with 
percaglobulin,  and  another  which  would  not.  Thus  the  hen  [Gallus 
domesticus)  with  i  -46  per  cent,  of  ovomucoid  gave  a  highly  positive 
reaction,  but  the  hawk  {Astur  palumbarius)  with  i  -45  per  cent,  gave 
none  at  all.  Preparations  of  ovomucoid  from  the  two  varieties  of 
egg-white  (see  Table  10  a)  did  not  show  up  the  existence  of  two  ob- 
viously different  chemical  individuals,  and  it  was  concluded  that  the 
preparations  were  in  each  case  mixed  with  a  small  amount  of  the 
other  substance.  Moreover,  of  the  egg-whites  which  gave  a  positive 
reaction  with  percaglobulin,  some  contained  ovomucoid  precipitable 
with  Esbach's  reagent  (e.g.  Clangula  glaucion  and  Somateria  mollissima) 
and  others  contained  an  ovomucoid  which  could  not  be  so  pre- 
cipitated (e.g.  Gallus  domesticus  and  Podiceps  cristatus).  It  is  quite 
uncertain  how  many  of  the  effects  observed  by  Morner  are  due  to 



[PT.  Ill 

physical  and  colloidal  rather  than  to  chemical  differences,  and  the 
whole  question  should  be  reinvestigated.  There  seemed  to  be  no 
special  significance  in  the  distribution  of  the  ovomucoid  which  was 
precipitable  by  percaglobulin ;  thus  it  was  present  in  the  accipitres, 
grallae,  lamellirostres,  longipennes  and  pygopodes,  but  not  in  the 
passeres,  zygodactyli,  pullastrae  and  steganopodes.  As  for  the  fowls, 
it  was  present  in  the  eggs  of  the  hen  and  pheasant,  but  not  in 
those  of  the  guinea-fowl.  Morner  was  inclined  to  agree  with  Milesi's 
view  that  ovomucoid  did  not  exist  as  such  in  the  natural  egg-white 
at  all. 

Table  14.    Variations  in  properties  of  avian  egg-white. 

Coagulation  point 

Consistency  and 

of  the 

egg-white  m 

colour  of  coagulum 

degrees  Fahrenheit 



Hard  white 




Pretty  firm,  bluish 



Soft,  white,  translucent . 


Missel  thrush 

Soft,  transparent 



Firm  white 



Soft  white 



Pretty  firm,  greenish, 


Golden-crested  wren 

Soft,    bluish,    semi-trans 


As  has  already  been  observed,  Sir  Thomas  Browne  was  one  of 
the  first  to  note  that  the  coagulated  egg-white  of  the  gull's  egg  was 
quite  different  in  consistency  and  translucency  from  that  of  the  hen's 
egg.  In  1863  Davy  collected  some  data  on  these  points,  which  are 
shown  in  Table  14,  and  Tarchanov  devoted  much  time  to  the 
question  in  the  'eighties  of  the  last  century.  He  found  that  the  whites 
of  many  kinds  of  eggs  would  not  coagulate  in  the  ordinary  way  on 
boiling,  but  either  remained  liquid  and  transparent  or  else  set  to  a 
watery  translucent  jelly.  This  he  called  "  tataeiweiss  ",  and  as  he  went 
on  to  examine  the  distribution  of  this  property  he  found  that  it  was 
associated  with  the  hatching  quality  of  the  bird  in  question.  Thus 
all  nidifugous  birds,  whose  chicks  are  born  fully  feathered  ("downy") 
and  soon  leave  the  nest,  had  eggs  with  ordinary  egg-white,  but  all 
nidicolous  ones,  whose  chicks  are  hatched  as  "squabs"  or  naked  and 
weak,  and  have  some  development  yet  to  complete,  had  eggs  with 
uncoagulable  or  transparent  egg-white.  Thus  the  sand-martin,  linnet, 
finch,  thrush,  canary,  crow,  dove,  rook,  nightingale,  robin,  starling 
(roughly  passeres  and  pullastrae),  all  had  tataeiweiss]  while  the  hen, 


duck,  goose,  guinea-fowl,  partridge  and  corncrake  had  ordinary 
white.  This  classification  agreed  roughly  with  Davy's  high  and  low 
coagulation  points  for  the  egg-white,  and  corresponded  on  the  whole 
to  Morner's  two  classes,  the  former  having  ovomucoid  not  precipit- 
able  with  percaglobulin  and  the  latter  having  the  precipitable 
variety,  but  to  this  there  were  some  exceptions;  thus  the  plover's 
ovomucoid  could  be  so  precipitated,  but  its  egg-white  was  tata 
and  it  yet  produced  fully-feathered  chicks.  It  was,  however,  the  only 
exception  to  Tarchanov's  generalisation,  (It  should  be  explained 
that  the  word  tata  was  derived  from  the  name  of  Tarchanov's  small 
daughter.)  Tarchanov  found  that  tata  egg-white  was  about  3  per 
cent,  richer  in  water  than  the  other  kind,  a  conclusion  which  Morner's 
later  analyses  did  not  confirm.  He  also  said  that  it  was  alkaline  to 
litmus,  but  became  less  so  as  the  tata  eggs  developed.  This  agrees 
with  the  later  classical  work  of  Aggazzotti  on  the  reaction  of  the  egg- 
white  of  the  hen's  egg  during  its  development.  Tarchanov  reported 
that  tata  egg-white  could  be  made  to  coagulate  at  ordinary  tempera- 
tures by  the  addition  of  a  little  potassium  sulphate,  and  that  it  would 
itself  coagulate  if  the  temperature  was  raised  well  above  the  boiling- 
point  of  water.  It  was,  he  said,  more  easily  digested  by  enzymes,  it 
putrefied  more  readily,  and  during  development  it  changed  into  a 
form  resembling  ordinary  egg-white.  He  made  some  studies  on  its 
secretion  by  the  oviduct  of  these  birds,  and  was  the  first  to  perform 
the  experim.ent  of  putting  a  ball  (in  his  case  a  lump  of  amber)  at 
the  top  of  the  oviduct  and  seeing  it  emerge  at  the  bottom  with  layers 
of  egg-white  and  a  shell  secreted  around  it.  The  change  during 
development  from  tata  to  ordinary  egg-white  Tarchanov  found  he 
could  imitate  by  bubbling  carbon  dioxide  through  the  original  white, 
after  which  it  would  coagulate  in  the  usual  way.  On  the  other  hand, 
he  found  that  if  he  soaked  normal  hen's  eggs  in  a  10  per  cent,  solu- 
tion of  alkali  the  white  took  on  the  properties  of  tata  egg-white,  and 
became  just  like  the  glassy  material  in  the  sand-martin's  egg.  He 
suggested  some  relation  between  these  phenomena  and  the  alkali- 
albuminate  of  Lieberkiihn,  but  did  little  to  determine  its  chemical 
relationships.  He  was  unable  to  get  any  development  in  the  case  of 
hen's  eggs  soaked  in  alkali. 

In  1 89 1  Zoth  took  up  the  whole  question  of  tataeiweiss  once 
more.  He  was  led  to  do  so  on  account  of  some  researches  which  he 
had  been  making  on  the  effect  produced  on  serum-clotting  by  various 

274  THE   UNFERTILISED   EGG   AS   A  [pt.  iii 

concentrations  of  alkali,  and  which  showed  that  the  clot  could  vary 
very  greatly  in  its  properties,  from  opacity  to  almost  perfect  trans- 
parency, for  instance.  Tarchanov  had  decided  that  the  transparent 
coagulum  of  the  nidicolous  egg-whites  was  not  to  be  identified 
with  that  produced  by  sodium  or  potassium  albuminate,  but  Zoth 
succeeded  in  showing  that  the  differences  were  not  sufficient  to  dis- 
tinguish them.  Zoth  fully  confirmed  Tarchanov's  finding  that  ordinary 
egg-white  could  be  made  to  pass  over  into  nidicolous  egg-white  by 
treating  it  with  i  o  per  cent,  potash  in  the  cold  for  ten  days,  and  was 
able  to  explain  all  the  differences  between  tataeiweiss  and  alkali 
ovoalbuminate  as  due  to  variations  in  the  amount  of  alkali  present, 
or  rather  the  amount  of  cation  as  compared  to  anion.  It  is  most 
unfortunate  that  we  have  no  detailed  ash  analyses  of  the  egg-whites 
of  nidicolous  birds,  for,  as  will  later  be  seen,  the  egg-white  of  the 
hen  has  rather  more  total  anion  than  total  cation,  and  this  relation- 
ship might  be  expected  to  be  even  more  strongly  marked  in  the  case 
of  nidicolous  egg-white,  perhaps^  indeed,  as  much  as  to  counter- 
balance the  excess  of  cation  over  anion  in  the  yolk.  There  can  be  no 
doubt,  however,  that  the  egg-whites  of  nidicolous  birds  are  relatively 
richer  in  alkali  than  are  those  of  others,  and  it  is  this,  combined  with 
their  different  water  and  total  ash  content,  which  causes  the  albumen 
to  coagulate  differently  from  those  of  others.  Thus,  if  5  c.c.  of  filtered 
egg-white  from  a  fresh  hen's  egg  be  put  in  each  of  three  small 
Erlenmeyer  flasks,  2  c.c.  of  water  added  to  A,  2  c.c.  of  0-89  per  cent. 
KOH  to  B,  and  2  c.c.  of  a  mixture  of  equal  parts  0-89  per  cent.  KOH 
and  0-66  per  cent.  NaCl  to  C,  the  coagulum  in  A  will  be  the  usual 
white,  thick,  solid  and  opaque  mass,  while  the  other  two  will  be 
transparent  like  tataeiweiss,  slightly  opalescent,  more  or  less  liquid,  and 
Cmore  opalescent  than  B.  It  would  be  interesting  to  reinvestigate  the 
whole  question  anew  in  the  light  of  recent  knowledge  and  technique. 

Another  curious  effect  was  noted  by  Melsens  and  Gautier.  Melsens 
found  that,  if  a  stream  of  carbon  dioxide,  hydrogen,  nitrogen  or 
oxygen,  was  passed  through  dilute  egg-white,  or  if  it  was  shaken 
violently,  a  precipitate  of  fibrous  membranous  shreds  was  formed. 
Gautier  observed  that  about  i  -5  per  cent,  of  the  protein  was  thus 
changed;  he  filtered  it  off  and  determined  its  elementary  composition, 
which  showed  nothing  remarkable.  He  concluded  that  a  protein 
which  he  called  "  ovofibrinogen "  existed  in  the  egg-white,  and  even 
suggested  that  an  "  ovo thrombin  "  was  present  to  turn  it  into  "ovo- 


fibrin".  He  apparently  thought  that  the  ovofibrin  was  incorporated 
without  change  into  the  substance  of  the  embryo.  The  subject  has 
not  received  any  attention  since  the  time  of  Gautier,  but  it  is  probable 
that  this  phenomenon  is  explained  by  the  work  of  Young;  Dreyer  & 
Hanssen  and  others,  on  the  high  instability  of  protein  solutions. 

Peptones  were  reported  by  Reichert  to  exist  in  fresh  egg-white. 

Wu  &  Ling  have  recently  studied  the  coagulation  of  ovoalbumen 
by  strong  mechanical  agitation.  The  fact  that  conalbumen  is  not 
coagulable  by  such  means  gave  them  a  method  of  estimating  it  in 
egg-white.  Thus  they  obtained  the  following  figures  for  Gallus 
domesticus  egg-white: 

Total  N  (ovoalbumen  +  conalbumen  4- ovomucoid)  1-71  gm.  % 

After  shaking  (conalbumen  +  ovomucoid)  ...  0-372      ,, 

After  shaking  and  heating  (ovomucoid)  ...  0-211      ,, 

Coagulation  of  ovoalbumen  by  shaking  was  not  separable  into  two 
stages  (denaturation  and  agglutination)  like  that  by  heat  or  alcohol. 
The  isoelectric  point  of  the  protein  was  the  most  favourable  for 
shaking  coagulation  (/?H  4-8)  and  the  Q^^q  of  the  reaction  was  i-g. 
Piettre  has  published  a  method  for  separating  the  proteins  which 
involves  the  use  of  acetone. 

The  relationships  between  the  avian  egg-white  proteins  have  been 
the  subject  of  some  interesting  immunological  work.  The  earliest 
investigators  who  crystallised  ovoalbumen  found  that  perfect  fresh- 
ness was  necessary,  for  at  room  temperature  the  crystallisable  protein 
gradually  turns  into  a  non-crystallisable  one.  Bidault  &  Blaignan 
found  that  this  process  could  be  arrested  by  placing  the  ^gg  at  0°. 
Sorensen  &  Hoyrup  suggested  that  the  protein  formed  was  conalbu- 
men and  wished  to  look  upon  the  latter  as  a  product  of  ovoalbumen. 
Hektoen  &  Cole,  however,  first  showed  that  though  ovoalbumen 
was  distinct  from  the  serum  albumen  of  the  hen  immunologically, 
conalbumen  was  not,  and  then  went  on  to  demonstrate  that  during 
the  loss  of  crystallisable  ovoalbumen  which  takes  place  as  the  egg 
ages,  there  was  no  corresponding  increase  in  conalbumen.  We  must 
therefore  look  upon  the  latter  as  probably  identical  with  the  serum 
albumen  of  the  adult:  and  perhaps  only  present  in  the  ^gg  owing  to 
the  inefficiency  of  the  oviduct. 

The  analyses  of  ovomucoid  and  Eichholz's  ovomucin,  as  well  as 
the  fragmentary  one  of  conalbumen,  will  be  found  in  Tables  i  o  a 
and  1 1 .  Willanen  found  that  ovomucoid  was  much  more  susceptible 


276  THE   UNFERTILISED   EGG  AS  A  [pt.  hi 

to  hydrolysis  by  pepsin  than  by  trypsin  (see  later  under  enzymes  and 
antitrypsin).  For  its  properties  see  the  papers  of  Morner  and  Neu- 
mann. Both  the  glucoproteins  have  twice  as  much  sulphur  as  ovo- 
albumen.  Their  carbohydrate  content  has  been  the  subject  of  a  great 
amount  of  discussion  and  experimental  work.  Berzelius  was  the 
first  to  draw  attention  to  certain  similarities  between  the  breakdown- 
products  of  sugars  and  proteins  when  acted  upon  by  boiling  acids. 
In  1876  Schiitzenberger  asserted  that  the  ovoalbumen  molecule 
contained  a  carbohydrate  group,  basing  his  views  on  positive  results 
with  Trommer's  test  after  total  hydrolysis.  In  later  years  a  number 
of  workers  supported  the  view  that  the  carbohydrate  was  glucose, 
using  in  different  cases  methods  of  varying  reliability,  e.g.  Kruken- 
berg  in  1885,  Hofmeister  and  Kravkov  in  1897,  and  Blumenthal ; 
Blumenthal  &  Mayer  and  Mayer  in  1898  and  1899.  Spencer  and 
Morner,  however,  failed  to  get  any  evidence  of  a  carbohydrate 
group  after  hydrolysis,  and  reported  their  negative  results  in  1898. 
Weiss,  about  the  same  time,  thought  he  could  identify  a  methyl 
pentose  among  the  hydrolysis  products,  but  he  was  never  confirmed. 
Seemann  was  the  first  to  announce  that  the  carbohydrate  was  glucos- 
amine, and  his  discovery  was  quickly  confirmed  by  Frankel  and 
Langstein.  These  later  workers  began  to  attempt  quantitative  estima- 
tion of  the  sugar,  and  their  figures  are  given  in  Table  15.  Pavy, 
using  the  then  recently  discovered  osazone  technique,  made  a  study 
of  a  variety  of  proteins,  and  showed,  as  might  be  expected,  that  the 
yield  from  ovoalbumen  was  always  greatly  less  than  from  ovomucoid. 
Eichholz  obtained  glucosazone  from  ovoalbumen,  ovom.ucoid  and 
ovomucin,  but  not  from  either  serum  albumen  or  casein.  On  the 
whole,  it  is  most  likely  that  ovoalbumen  contains  extremely 
little  glucosamine,  and  the  figures  recorded  in  the  literature  for 
this  are  probably  due  to  contamination  with  ovomucin.  This  is  the 
view  of  Osborne,  Jones  &  Leavenworth,  for  neither  they  nor 
Osborne  &  Campbell  obtained  any  glucosamine  from  their  very 
carefully  purified  ovoalbumen.  Komori  has  prepared  from  ovo- 
mucoid, and  Frankel  &  Jellinek  from  ovoalbumen,  polysaccharide- 
like  substances  which  they  regard  as  the  prosthetic  group  containing 
all  the  glucose.  Following  this  up  Levene  &  Mori  have  prepared  a 
trisaccharide  containing  glucosamine  and  mannose  from  egg-white. 
Ovoalbumen  contains  0-26%  of  this  substance,  coagulated  egg-white 
1*9%,  and  ovomucoid  5*1%.    According  to  Levene  &  Rothen  the 

SECT.   l] 



molecule  consists  of  four  trisaccharides  each  containing  one  molecule 
of  glucosamine  and  two  of  mannose. 

Table  15.    Ovoalbumen  and  ovomucoid  glucosamine  content. 

Hen  {Callus  domesticus) 

Hofmeister  (1898) 

Seemann  (1898)  ... 

Langstein  (1900) 

Willanen  (1906)  ... 

Pavy  (1907)  

Samuely  (1911)   ... 

Neuberg  &  Schewket  (1912)     ... 

Zeller  (1913)        

Needham  (1927) 

Abderhalden,  Bergell  &  Dorpinghaus 

Neuberg  (i 901)  ... 

Blumenthal  &  Mayer  (1900)     ... 

Izumi  (1924) 

Tillmans  &  Philippi  (1929) 
Turtle  ( Thalassochelys  corticata) 

Takahashi  (1929) 

Bywaters  (1909)  Seromucoid 
Pavy  (1899)         Ovomucoid 













Glucose  %  by  hydrolysis  with 

Osseomucoid  ... 
Tendon  mucoid 
Ovoalbumen  ... 
Serum  globulin 

10  %  KOH 




5  %  HCl 





The  free  carbohydrate  of  the  egg-white  has  also  received  a  great 
amount  of  attention  from  an  early  date.  In  1846  Winckler  isolated 
a  quantity  of  a  sugar  (4  grains)  from  the  egg-white  of  the  hen's  egg, 
and  identified  it  as  lactose.  ''Physiologists",  he  said,  "will  be  able 
to  tell  me  whether  this  is  of  importance  for  the  embryo  or  whether 
it  was  some  abnormality."  The  observation  has  not  since  been  re- 
peated, and  it  is  in  the  highest  degree  unlikely  that  any  lactose  was 
ever  in  an  egg,  unless  the  diet  of  the  hen  was  a  very  unusual  one. 
Budge  and  Aldridge  soon  were  at  work  on  this  subject,  the  former 
concluding  that  the  carbohydrate  was  glucose,  but  suggesting  that 
it  might  form  a  disaccharide  during  development,  and  the  latter 
making  no  concession  to  Winckler.  The  presence  of  glucose  was 
afterwards  abundantly  established  by  the  work  of  Barreswil ;  Leh- 
mann ;  Meissner ;  Salkovski ;  and  Pavy.  Later  many  quantitative 
estimations  were  made,  and  these  are  collected  together  in  Table  16. 
The  older  figures  for  free  carbohydrate  may  be  regarded  as  fairly 








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28o  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

trustworthy,  but  not  for  combined  sugar,  in  view  of  the  demonstra- 
tion of  Holden  that  all  copper-reducing  methods  are  seriously  inter- 
fered with  by  the  presence  of  amino-acids  and  protein  breakdown 
products.  No  method  at  present  in  use  gives  satisfactory  results  in 
those  conditions,  but  the  most  reliable  is  that  of  Hagedorn  & 
Jensen.  No  estimations  of  total  carbohydrate  in  egg-white  alone  at 
present  exist,  but  there  is  a  single  figure  for  glycogen  due  to  Sakuragi. 
Morner  found  no  evidence  of  fructose,  pentoses  or  maltose. 

A  curious  phenomenon :  the  fluorescence  of  egg-white  has  been 
reported  by  van  Waegeningh  &  Heesterman,  but  it  only  occurs  if 
the  egg  is  not  perfectly  fresh,  and  is  therefore  probably  not  physio- 

I '7.    The  Avian  Yolk 

The  vitelline  membrane  was  investigated  by  Liebermann  in  il 
who  found  that  it  consisted  almost  exclusively  of  keratin.  This  he 
purified,  and,  having  freed  it  from  ash,  made  an  elementary  analysis 
of  it,  which  is  shown  in  Table  loa.  Some  experiments  which  demon- 
strate the  peculiarities  of  the  vitelline  membrane  have  been  devised 
by  Osborne  &  Kincaid.  They  found  that  a  fresh  yolk  floated  into 
distilled  water,  o-g  per  cent.  NaCl  solution,  or  glycerol,  behaved 
exactly  like  a  red  blood  corpuscle  in  that  it  swelled  up  and  burst 
in  the  former,  and  shrank  to  a  corrugated  globe  in  the  latter,  while 
in  the  isotonic  salt  solution  it  remained  unchanged.  But  with  other 
treatment,  nothing  took  place  which  corresponded  to  haemolysis.  If 
the  yolk  was  put  into  lo  per  cent.  NaCl  solution,  it  did  not  shrink, 
as  had  been  expected,  but  swelled  up,  owing  to  the  penetration  of 
the  saline  and  the  consequent  osmotic  pressure  due  to  the  dissolving 
of  the  vitellin  in  the  saline.  This  showed  at  once  the  scleroprotein 
nature  of  the  membrane  and  its  impermeability  to  vitellin  even  when 
in  solution.  The  membrane  is  also  impermeable  to  phosphatides  and 
fats  dissolved  in  ether,  for  if  a  yolk  is  put  into  ether  it  sinks  and  swells, 
so  that  the  upper  pole  is  distended  by  an  accumulation  of  deeply 
pigmented  ether.  But  until  the  yolk  bursts,  as  it  eventually  does, 
not  a  trace  of  pigment  or  other  substance  passes  out  into  the  ether, 
and  the  same  results  were  found  with  chloroform  and  carbon  disul- 
phide.  In  alcohol,  on  the  other  hand,  there  is  no  swelling,  for  the 
alcoholic  solution  of  phosphatides  and  other  bodies  can  pass  out 


through  the  keratin  membrane.  It  would  be  very  interesting  to  make 
a  more  extended  study  of  the  osmotic  properties  of  the  vitelline 
membrane  (see  in  this  connection  Section  5*6). 

The  yolk  of  the  egg  was  investigated  earlier  in  the  modern  period 
than  the  white.  We  may  pass  directly,  excluding  the  curious  analysis 
of  the  eggs  of  Struthio  casuarius  by  Holger  in  1822,  to  the  papers  of 
Gobley,  which  appeared  from  1846  to  1850,  and  which,  with  those 
of  Valenciennes  &  Fremy  from  1854  to  1856,  still  remain  models 
of  embryo-chemical  work.  "John,  a  German  chemist,"  said  Gobley, 
"appears  to  have  been  the  first  to  occupy  himself  with  serious 
researches  on  the  yolk  of  the  egg.  The  chemists  who  preceded  him 
considered  it  as  made  up  only  of  water,  albumen,  oil,  gelatine,  and 
colouring  matter;  such  was  the  opinion  of  Macquer,  Fourcroy,  and 
Thomson.  John  concluded  from  his  experiments,  which  he  published 
in  181 1,  that  the  yolk  was  composed  of  water,  a  sweet  yellow  oil, 
traces  of  a  free  acid  which  he  thought  was  phosphoric  acid,  and  a 
small  amount  of  a  brownish  red  substance,  soluble  in  ether  and 
alcohol.  Besides  these  he  found  gelatine,  sulphur,  and  a  great  deal 
of  a  modified  albuminous  substance."  Gobley  referred  also  to  the 
work  of  Prout,  of  Chevreul,  of  Berzelius  and  of  Lecanu,  who  dis- 
covered the  presence  of  cholesterol  in  yolk  in  1829. 

Gobley  himself  found  in  the  yolk  nearly  all  the  substances  which 
we  now  know  to  be  there.    His  own  list  of  them  ran  as  follows : 

1 .  Water. 

2.  An  albuminous  matter,  "vitellin", 

3.  Olein. 

4.  Margarin. 

5.  Cholesterin. 

6.  Margaric  acid. 

7.  Oleic  acid. 

8.  Phosphoglycerilic  acid. 

9.  Lactic  acid. 

10.  Salts  such  as  chloride  of  sodium,  chloride  of  potassium,  chlorhydrate 

of  ammonium,  sulphate  of  potash,  phosphate  of  lime,  and  phos- 
phate of  magnesia. 

11.  A  yellow  colouring  matter  and  a  red  colouring  matter. 

12.  An  organic  substance  containing  nitrogen,  but  which  is  not  al- 


Most  of  the  constituents  of  egg-yolk  may  be  recognised  under  this 






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284  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

old-fashioned  terminology.  Gobley  made  many  quantitative  observa- 
tions on  the  various  substances,  and  his  figures  are  given  in  Table  17, 
which  sums  up  all  the  analyses  that  have  been  made  of  the  yolk 
in  the  eggs  of  birds.  The  original  discovery  of  vitellin  was  made  by 
Dumas  &  Cahours,  but  Gobley  was  the  first  to  make  an  extended 
study  of  it.  His  elementary  analysis  is  given  in  Table  10  a.  He  knew 
that  it  contained  both  sulphur  and  phosphorus.  Gobley  was  able  to 
isolate  oleic  and  margaric  (palmitic)  acids  from  the  fat  fraction  of 
the  yolk,  but,  unlike  Planche  twenty-five  years  before,  he  got  no 
stearic,  and  Kodweiss,  one  year  later,  reported  its  presence  under 
the  impression  that  it  had  not  been  found  before.  Gobley,  however, 
was  easily  able  to  repeat  Lecanu's  discovery  of  the  presence  of 
cholesterol,  and  made  a  remarkable  examination  of  the  lipoids. 
"These  viscous  materials",  he  said,  "appear  to  have  been  considered 
by  John  as  not  being  of  a  fatty  nature  at  all.  They  form  the  most 
interesting  part  of  the  yolk;  they  contain  all  the  phosphorus  which 
exists  there  in  considerable  quantity."  He  analysed  the  glycero- 
phosphoric  acid  which  he  obtained  from  the  lipoid,  which  he  named 
"lecithin",  and  speculated  as  to  the  significance  which  it  might  have 
for  the  growth  of  the  embryo.  He  also  recognised  that  fatty  acids 
and  nitrogen  were  present  in  the  viscous  matter. 

Ten  years  later  Valenciennes  &  Fremy  made  a  further  examina- 
tion of  the  yolks  of  a  large  variety  of  eggs  with  special  reference  to 
\itellin.  It  was  they  who  discovered  substances  very  similar  to  vitellin 
in  the  eggs  of  reptiles  and  fishes;  these  they  named  the  ichthulins. 
As  regards  the  eggs  of  birds,  they  contented  themselves  with  con- 
firming the  results  of  the  previous  in\'estigators,  but  they  regarded 
vitellin  as  having  practically  the  same  constitution  as  fibrin,  on  the 
grounds  of  elementary  composition  only.  At  the  same  time,  they  held 
it  to  be  a  different  compound  because  it  would  not,  like  blood  fibrin, 
decompose  hydrogen  peroxide. 

If  Table  1 7  is  examined,  it  will  be  seen  that  the  yolk  is  much  drier 
than  the  white  in  all  birds'  eggs  examined,  having  only  about  50  per 
cent,  of  water  as  against  the  85  per  cent,  of  the  latter.  On  the  other 
hand,  the  percentage  of  fatty  substances  and  lipoids  is  much  higher, 
being  just  about  double  the  amount  of  protein,  whether  related  to 
wet  weight  or  to  dry.  It  is  noticeable  from  the  analyses  of  Tarchanov 
that  the  yolks  of  eggs  from  nidicolous  birds  having  a  short  incubation 
time  are  about  10  per  cent,  richer  in  water  than  yolks  from  the  eggs 


of  nidifugous  birds.  This  must  imply  that  the  greater  requirement 
for  nutrient  material  in  the  latter  case  has,  as  it  were,  packed  the 
fat  tighter  into  the  yolk.  Exactly  the  same  relationship  is  brought 
out  from  the  figures  of  Spohn  &  Riddle,  who  compared  the  pigeon 
which  hatches  out  as  a  squab  with  the  hen  which  hatches  out  as  a 
fully-feathered  chick.  Spohn  &  Riddle's  analyses  are  the  only  com- 
plete ones  we  have  for  a  nidicolous  egg,  and  bear  clearly  the  same 
relationship,  for  there  is  less  protein  and  less  fat,  relatively,  in  the 
pigeon's  egg  than  in  the  hen's.  The  ash  content  and  the  amount  of 
non-nitrogenous  extractive  substances  seem,  however,  to  be  slightly 
higher  in  the  latter  case.  Langworthy's  figures  were  all  obtained 
from  the  eggs  of  nidifugous  birds,  and  they  show  a  great  similarity 
among  themselves.  More  delicate  consideration,  of  course,  reveals 
differences  according  to  breed  in  the  hen's  egg,  e.g.  the  figures  of 
Pennington  and  his  collaborators,  but  these  are  of  a  comparatively 
minor  order. 

The  most  interesting  analyses  are  those  of  Spohn  &  Riddle.  They 
compared  the  egg  of  the  jungle-fowl,  which  is  supposed  to  have  been 
the  evolutionary  ancestor  of  the  domestic  hen,  with  averaged  figures 
for  hen's  eggs  of  various  breeds,  and,  as  is  evident,  there  was  a  very 
close  agreement.  They  also  analysed  the  white  yolk  as  distinct  from 
the  yellow  yolk  of  the  hen's  tgg.  When  the  yolk  begins  to  be  formed 
in  the  ovary  of  the  hen,  it  is  white  and  not  yellow,  and  not  until 
the  critical  point  in  its  maturation  is  reached,  when  its  growth-rate 
completely  changes,  does  it  begin  to  store  lipochrome  pigment.  This 
change  in  growth-rate,  which  has  been  observed  by  other  workers 
as  well  as  Riddle  (e.g.  Walton),  will  be  dealt  with  in  more  detail 
in  the  appendix  on  maturation.  Von  Hemsbach,  in  a  paper  on  the 
milky  or  white  yolk  of  the  birds,  in  1851,  suggested  that  the  corpus 
luteum  of  mammals  corresponded  to  the  yellow  yolk  of  birds,  and 
that  the  mammalian  ovum  having  been  shed  out  of  the  ovary  into 
the  Fallopian  tube  and  uterus,  the  fats  and  lipochrome  pigment 
were  laid  down  in  the  Graafian  follicle  instead  of  around  the  white 
*'ovum".  Von  Hemsbach  also  supported  the  view  already  mentioned 
that  the  shells  of  avian  and  amphibian  eggs  corresponded  to  the 
decidua  of  mammals.  He  laid  stress  on  the  work  of  Zwicky  and 
Gobel,  who  had  investigated  the  pigments  of  yolk  and  corpus  luteum, 
and  had  thought  them  to  be  identical.  This  subject  will  be  referred 
to  again  under  the  head  of  pigments. 



286  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

In  the  fresh  egg,  as  laid,  the  white  yolk  occupies  a  central  position, 
and  is  surrounded  by  concentric  layers  of  yellow  yolk.  But  as  a  kind 
of  cylindrical  prolongation  of  the  white  yolk  reaches  to  the  surface 
of  the  vitellus  underneath  the  blastodisc  or  germinal  spot,  the  white 
yolk  must  be  considered  the  first  food  of  the  embryo,  and,  until  its 
composition  was  determined,  it  was  not  possible  to  say  what  sort 
of  nutrient  environment  the  embryo  possessed  in  the  very  early  days 
of  development,  although  the  composition  of  the  yellow  yolk  would 
give  this  for  the  later  period.  The  histological  differences  between 
white  and  yellow  yolk  had  been  known  for  a  long  time  (see  Purkinje ; 
His ;  Leuckart ;  Klebs ;  Dursy ;  Strieker ;  and  Virchow)  but  Riddle 
and  Spohn  &  Riddle  were  the  first  to  approach  the  subject  chemically. 
Their  figures  showed  that  the  white  yolk  much  the  more  nearly 
approximated  to  the  contents  of  invertebrate  eggs  with  holoblastic 
cleavage,  and  living  undifferentiated  tissue  generally.  Instead  of  45  per 
cent,  of  water,  the  white  yolk  had  86  per  cent.,  instead  of  15  per  cent, 
of  protein,  it  had  only  4,  and  instead  of  25  per  cent,  of  fat  it  had 
only  2.  Thus  in  its  water-content,  it  was  much  more  like  {a)  egg- 
white  and  {b)  the  young  embryo  itself  than  like  ordinary  yolk,  while 
instead  of  having  twice  as  much  fat  as  protein  it  had  twice  as  much 
protein  as  fat.  These  data  are  extremely  interesting  in  view  of  the 
facts  that  are  known  about  the  sources  of  energy  made  use  of  by  the 
embryo  during  its  development.  Although  by  far  the  greatest  pro- 
portion by  weight  of  substance  combusted  during  embryonic  life  is 
fat,  yet,  in  the  early  stages,  the  embryo  undoubtedly  gets  its  energy 
preponderantly  from  protein  and  carbohydrate  (see  the  whole  of 
Section  7).  The  percentage  of  non-nitrogenous  extractives  did  not 
differ  much  between  white  and  yellow  yolk  in  the  experiments  of 
Spohn  &  Riddle,  but  it  would  be  very  interesting  to  know  the 
relative  amounts  of  carbohydrate,  and  analyses  to  discover  this  should 
certainly  be  done.  Again,  the  yellow  yolk  contained  eight  times  less  ash 
than  the  white  yolk,  a  finding  which  acquires  considerable  significance 
from  the  fact  that,  if  the  ratio  inorganic  substance/organic  substance 
in  the  embryonic  body  is  plotted,  it  is  seen  to  descend  steadily 
from  the  beginning  of  development  (see  Fig.  249).  Moreover,  as 
Mendeleef  has  shown,  early  embryonic  cells  contain  twice  as  much 
electrolyte  as  those  of  later  stages  (see  Section  5"8).  The  amount  of 
phosphatide  in  the  yellow  yolk,  furthermore,  was  ten  times  that  in 
the  white,  a  significant  difference;  for,  as  Plimmer  &  Scott  have  shown, 


one  of  the  main  functions  of  the  phosphatide  is  in  furnishing  phos- 
phorus for  the  embryonic  bones  during  the  period  of  ossification,  a 
requirement  which  is  not  present  in  the  earher  stages  of  the  develop- 
ment. The  histochemical  work  of  Marza,  who  compared  the  white 
and  yellow  yolk  following  the  method  of  Romieu,  is  in  agreement 
with  this,  for  he  found  the  elements  of  the  yellow  yolk  to  be  richer 
than  those  of  the  white.    (See  Plate  X.) 

1-8.    The  Avian  Yolk-proteins 

As  regards  the  protein,  vitellin  (Tables  10 a  and  11),  several  interest- 
ing points  are  to  be  observed.  The  best  elementary  analyses  of  ovo- 
vitellin are  probably  those  of  Osborne  &  Campbell.  After  its  discovery 
by  Dumas  &  Cahours,  Gobley,  and  Valenciennes  &  Fremy,  it  was 
studied  by  Hoppe-Seyler,  and  now  for  the  first  time  with  special  refer- 
ence to  its  position  in  the  classification  of  the  proteins.  Virchow  had  some 
time  before  then  suggested  that  the  yolk-platelets,  familiar  to  histolo- 
gists,  contained  lecithin,  and  there  had  been  some  doubt  as  to  their 
nature.  Valenciennes  &  Fremy  had  opposed  the  view  that  they  were 
crystals,  basing  their  view  on  Sennarmont's  work,  but  Radlkofer  and 
Hoppe-Seyler  returned  to  the  crystal  theory.  Hoppe-Seyler  believed 
that  vitellin  contained  no  phosphorus,  but  that  what  appeared  in  the 
analyses  was  due  to  contamination  with  lecithin.  This  view  was  sup- 
ported also  by  his  assistant,  Diakonov,  who  contributed  to  the  Med.Chem. 
Untersuchungen  one  of  the  earliest  investigations  of  phosphatide.  But  at 
the  same  time  Miescher  obtained  from  the  yolk  of  the  hen's  egg  a  sub- 
stance containing  a  great  deal  of  phosphorus,  and  possessing  certain 
of  the  properties  of  a  protein.  This  he  believed  to  be  nuclein.  "It  is 
interesting  ",  he  said,  "in  relation  to  the  origin  of  nuclear  substance, 
that  the  nutrient  yolk  contains  ready-formed  nuclein  in  significant 
quantity."  At  this  time,  then,  the  proteins  of  the  yolk  were  believed 
to  be  ovoglobulin  (for  so  Hoppe-Seyler  called  the  vitellin  of  the 
earlier  workers)  and  Miescher's  nuclein.  Miescher  himself  identified 
his  nuclein  as  a  constituent  of  the  white  yolk  of  the  histologists,  but 
he  noted  that  the  hen's  egg  seemed  to  have  no  xanthine  in  it. 

Lehmann,  Schwarzenbach  and  others,  however,  did  not  agree  with 
this  classification,  and  regarded  vitellin  as  a  mixture  of  albumen 
and  casein.  They  did  so  not  on  the  grounds  of  its  containing  phos- 
phorus, but  because  they  found  that  rennin  would  completely 
coagulate  it  from  its  pure  solution.  But  this  attitude  did  not  prevail. 

288  THE   UNFERTILISED   EGG    AS  A  [pt.  iii 

and  the  word  "  nucleovitellin "  became  general,  until  Kossel  in  1886 
found  that,  if  vitellin  was  really  a  nuclein,  it  differed  from  all  other 
such  substances  by  giving  no  trace  of  xanthine  after  acid  hydrolysis. 
On  the  other  hand,  true  nuclein,  he  found,  was  present  by  the  tenth 
day  of  development.  Hall  and  Burian  &  Schur,  Bessau  and  von 
Fellenberg  confirmed  this  absence  of  purines  from  the  fresh  egg.  In 
more  recent  times,  Sendju  and  Mendel  &  Leavenworth  have  found 
exceedingly  small  amounts  of  true  nucleoprotein  (2  and  i*6  mgm. 
per  cent,  respectively  wet  weight)  in  the  hen's  egg  (by  purine  bases), 
and  Plimmer  &  Scott,  and  Heubner  &  Reeb  have  done  the  same  (by 
phosphorus  analysis) .  Shortly  after  Kossel's  work,  Milroy  found  that 
vitellin  gave  a  biuret  test  though  no  Millon,  and  materially  differed 
in  nitrogen  and  phosphorus  content  from  any  of  the  nucleoproteins, 
while,  at  the  same  time,  Miescher  admitted  that  he  could  not  isolate 
any  purine  bases  from  his  "nuclein"  in  the  hen's  egg.  Levene 
&  Alsberg  next  investigated  the  manner  of  breakdown  of  vitellin, 
finding  the  substance  they  named  "  paranuclein  "  after  digestion  with 
pepsin,  and  "avivitellic  acid"  after  hydrolysing  with  ammonia.  The 
elementary  composition  of  these  substances  is  given  in  Table  10  a, 
from  which  it  could  be  seen  that  the  increasing  phosphorus  content 
implied  the  presence  of  phosphorus  as  an  important  constituent  of 
the  original  molecule.  Six  years  later  Levene  &  Alsberg  ascertained 
the  amino-acid  distribution  (see  Table  11).  They  pointed  out  the 
significance  of  the  high  proline  figure,  in  view  of  the  task  of  haemo- 
globin synthesis  which  the  young  embryo  has  before  it.  Abderhalden 
&  Hunter  and  Hugounenq  undertook  a  like  investigation  in  the  same 
year,  from  which  a  striking  similarity  between  the  amino-acid  dis- 
tribution in  vitellin  and  casein  came  to  light,  especially  as  regards 
the  high  proportion  of  leucine  and  glutamic  acid.  They  drew  atten- 
tion to  the  similarity  in  physiological  requirements  as  between  the 
"erste  Nahrung"  of  chick  and  mammal.  The  historical  associations 
of  this  discovery  have  already  been  referred  to  (see  p.  53).  It  was 
at  this  time  that  Neuberg,  and  Blumenthal  &  Mayer  reported  the 
existence  of  glucosamine  in  the  vitellin  molecule,  two  observations 
which  stood  together  in  isolation,  until  in  1929  Levene  &  Mori 
isolated  from  egg-yolk  the  same  trisaccharide  which  they  found  to 
be  present  in  ovoalbumen  and  ovomucoid  and  which  has  been  re- 
ferred to  above. 

It  was  not  until  the  paper  of  Bayliss  &  Plimmer  in  1906  that  the 



/  kj^EHHHH^^^HHI 

'  '^  " 


Stain,  haemalum-eosin:   magnification,   gxA:    prepared  and    microphotographed    by 
Dr  V.  Marza.  The  stratification  of  the  yolk  into  white  and  yellow  is  beginning. 


nature  of  vitellin  really  became  clear.  They  subjected  casein 
and  vitellin  to  the  action  of  trypsin,  and  studied  the  time  taken  under 
varying  conditions  for  the  phosphorus  to  be  split  off  into  soluble 
form.  Ovovitellin,  they  found,  was  much  more  slowly  digested  than 
casein,  for  after  36  days  only  half  of  its  phosphorus  had  been  made 
soluble,  whereas  after  2  or  3  days  a  large  percentage  of  the  casein 
phosphorus  had  gone  into  solution  in  inorganic  form,  and  most  of 
the  rest  was  present  in  water-soluble  organic  combination,  i  per 
cent,  soda,  however,  would  bring  aU  the  phosphorus  of  casein  into 
solution  in  24  hours.  BayUss  &  Plimmer  concluded  that  ovovitellin 
and  casein  were  both  phosphoproteins,  as  distinguished  from  nucleo- 
protein,  where  the  phosphorus  would  be  present  in  the  prosthetic 
group  and  not  in  the  protein  itself  Plimmer  &  Scott  later  found  that 
ovovitellin  behaved  in  the  same  way  to  soda.  This  reaction  served 
to  distinguish  between  phosphoproteins  and  nucleoproteins,  for  all 
the  latter,  it  was  found,  were  stable  to  alkali  and  easily  split  by 
acids.  From  the  phosphorus  distribution  in  the  unincubated  hen's 
egg,  Plimmer  &  Scott  concluded  that  vitelHn  accounted  for  at 
least  30  per  cent,  of  the  phosphorus,  and  this  led  them  on  to  their 
investigation  of  the  changes  which  take  place  in  the  different 
phosphorus  fractions  during  the  development  of  the  embryo. 

The  distribution  of  phosphorus-containing  compounds  in  egg-yolk, 
as  Plimmer  &  Scott  found,  makes  a  very  different  picture  from  that  of 
any  other  tissue.  Their  summary  is  shown  in  the  accompanying  table 
(18).  It  would  be  extremely  interesting  to  investigate  the  phosphorus 
distribution  in  the  white  yolk,  which  at  present  is  altogether  uncharted. 

Table  18.   Phosphorus  in  per  cent,  of  the  total  phosphorus. 









Lecithin  P    ... 





Total  water-soluble  P 





Water-soluble  inorganic  P 





Nucleoprotein  P 





Phosphoprotein  P    ... 





Total  protein  P 





The  third  of  these  fractions  i 

includes  the  phosph 

orus  of  all  unstable  water-soluble  corn- 


Steudel,  Ellinghaus  &  Gottschalk  have  recently  found  that  vitellin 
behaves  towards  pepsin  exactly  like  casein.  The  rate  of  increase  of 
titratable  COOH  groups  during  the  digestion  far  exceeds  that  of 
NH2  groups,   reaching  a  maximum  about  the  fourth  hour.   The 




[PT.  Ill 

Table  19. 

Per  cent,  of  dry  weight 

Total  N 



N/P  rati 

mer's  figures. 

Ovovitellin  ... 
ovolivetin     ... 
Ovoalbumen    ... 
Casein  ... 

...      15-29 

•••     15-51 
...      15-30 





Levene  &  Alsberg's  figures. 

Avivitellic  acid  ...      13-13 

Swigel  &  Posternak's  figures. 


Swigel  &  Posternak's  figures. 

Hydrolysis  of  ovotyrine  b^  (% ) 
H3PO4  acid  NH3  Arginine      Histidine        Lysine 

12-00  1-60  4-90  0-62  0-70  0-75 


Ovotyrine  a^    ... 

...      10-87 




Ovotyrine  ^^   ... 

...      11-33 




Ovotyrine  /Sj    ... 

...      10-92 




Ovotyrine  71    ... 






Table  20.    Nitrogen  distribution. 

Plimmer's  figures  (1908). 

Per  cent  of  dry  weight 


Ovovitellin    . 
Ovolivetin     . 













amino  N 

linkages  must  break,  therefore,  between  a  carboxyl  group  and  pro- 
line, tr-yptophane,  histidine  or  arginine. 

Weyl ;  v.  Moraczevski ;  and  Gross  were  the  first  to  describe  the 
properties  of  the  egg-yolk  proteins,  but  the  standard  account  is  that 
of  Plimmer,  who  in  1908  identified  two  yolk-proteins,  ovovitellin, 
and  ovolivetin.  Ovovitellin,  according  to  his  analyses,  contained 
1*0  per  cent,  of  phosphorus,  but  ovolivetin  only  o-i  per  cent.  He  was 
usually  able  to  isolate  far  more  of  the  former  than  the  latter,  but  in 
some  experiments  the  yield  seemed  to  be  nearly  equal.   Livetin  was 

SECT.   l] 



soluble  in  water  as  well  as  10  per  cent,  salt  solution,  but  it  cannot  be 
ovoalbumen  or  any  of  the  egg-white  proteins,  for  it  is  not  coagulated 
by  ether.  Plimmer  suggested  that  possibly  livetin  was  vitellin  with 
the  majority  of  the  phosphorus-containing  parts  split  off  from  it. 
Tables  19,  20  contain  Plimmer's  figures  for  these  two  proteins. 

Table  21. 


May  &  Rose 

Folin  &  Looney 

(1922),  (%) 

(1922),  (%) 






















Free  tryptophane  (%  of  whole  egg) 

von  Fiirth 

&  Lieben 

Ide  (1921) 


Whole  egg-contents 








"otal  tryptophane. 

(%  of  proteins) 

(%  of  proteins) 

Whole  egg-contents 









Whole  egg-contents 



Ovovitellin  has  been  the  subject  of  recent  investigations  by  Swigel 
&  Posternak.  They  found  that  it  broke  up  into  three  polypeptides 
which  they  call  ovotyrine  a^,  ^^  and  y^.  The  properties  of  these  are 
listed  in  Table  19.  It  was  found  that  ovotyrine  ^  contained  all  the 
iron  in  the  original  compound,  and  that  it  could  be  split  up  into 
ovotyrine  /Sj  and  ovotyrine  ^2  the  second  of  which  again  contained 
all  the  iron.  All  these  derivatives  were  laevorotatory,  and  showed 
considerable  resemblance  to  the  lactotyrines  which  the  same  workers 
had  previously  isolated  from  casein.  They  identified  their  ovotyrine  ^ 
with  the  avivitellic  acid  of  Levene  &  Alsberg,  and  they  stated  that 
an  enzyme  was  present  in  the  fresh  yolk  which  would,  on  standing 
at  37°  C.  for  10  days,  double  the  yield  of  preformed  ovotyrine  jS. 


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294  THE   UNFERTILISED   EGG  AS  A  [pt.  iii 

Hydrolysis  of  ovotyrine  ^  revealed  the  presence  of  large  amounts 
of  /-serine,  an  amino-acid  which  had  not  previously  been  found  in 
ovovitellin  (see  e.g.  Plimmer  &  Rosedale's  analyses).  Some  pyruvic 
acid  and  ammonia  being  given  off  as  well,  Swigel  &  Posternak 
calculated  that,  supposing  these  arose  from  breakdown  of  serine, 
there  would  have  been  sufficient  serine  present  initially  to  combine 
with  for  all  the  phosphorus.  They  therefore  suggested  that  the  main 
phosphorus-containing  unit  of  ovovitellin  was  serine-phosphoric  acid. 

Cohn,  Hendry  &  Prentiss  consider  the  minimal  molecular  weight 
of  vitellin  to  be  192,000,  i.e.  much  higher  than  ovoalbumen. 

Kay  &  Marshall  have  also  studied  the  yolk-proteins.  They  have 
prepared  purer  samples  of  vitellin  and  livetin  than  those  of  any 
previous  worker,  and  have  been  able  to  free  the  former  almost 
entirely  from  contamination  with  ovolecithin.  Their  vitellin  is  a  true 
phosphoprotein  containing  i  -3  per  cent,  of  phosphorus  and  hydrolysed 
by  I  per  cent,  soda,  though  not  by  the  phosphatase  of  the  kidney. 
Their  livetin  is  a  pseudo-globulin,  containing  only  the  slightest 
traces  of  phosphorus  (less  than  0-05  per  cent.).  The  yolk  of  the 
fresh  egg  contains  no  albumen.  Vitellin,  hydrolysed  with  dilute 
ammonia,  gives  a  vitellinic  acid  containing  about  10  per  cent,  of 
phosphorus.  Kay  has  estimated  the  cystine,  tryptophane  and  tyrosine 
in  vitellin  and  livetin  (Table  11);  in  the  latter  protein  they  are  dis- 
tinctly high  in  amount,  a  fact  of  some  importance  in  embryonic 
nutrition.  The  relative  amounts  of  vitellin  and  livetin  in  yolk  would 
appear  to  be  of  the  order  of  3-6  to  i  for  the  hen  and  3-8  to  i  for  the 
duck,  calculating  from  their  nitrogen  content.  Kay  regards  livetin 
as  identical  with  Gross'  protein.  The  yolk  of  a  fresh  egg  would 
contain  from  600  to  900  mgm. 

1*9.    The  Fat  and  Carbohydrate  of  Avian  Yolk 

The  fatty  acids  of  the  yolk  have  been  much  investigated  since  the 
time  of  Gobley  and  Kodweiss,  but  little  has  been  added  to  our  know- 
ledge of  them.  Paladino  found  olein,  palmitin  and  stearin  to  be 
present.    Analytical  details  are  in  Table  22. 

A  large  part  of  the  study  of  phosphatides,  under  the  generic  name 
of  lecithin,  has  been  made  on  that  obtained  from  the  yolk  of  the  egg; 
thus  the  work  of  Diaconov,  who  showed  it  contained  no  neurine, 
Strecker,  who  discovered  the  presence  of  choline,  Bergell ;  Cousin ; 
Laves  &  Grohmann;  Laves;  Wintgen  &  Keller;  Erlandsen;  Stern 


&  Thierfelder;  Frankel  &  Bolaffio  (whose  egg-yolk  neottin  was  only 
a  mixture  of  sphingomyelin  and  cerebrosides),  McLean;  Serono  & 
Palozzi;  Eppler;  Riedel;  Wilson,  and  Trier,  who  prepared  amino- 
ethylalcohol  from  it,  all  comes  under  this  heading.  In  McLean's 
book  will  be  found  a  review  of  it.  Certain  aspects  of  it,  however,  are 
important  here ;  for  instance,  the  question  of  the  presence  of  very 
unsaturated  acids  in  ovolecithin.  McLean  in  1909  found  stearic  and 
oleic  acids  in  it,  but  Cousin  was  able  to  isolate  linolenic  and  palmitic 
as  well,  and  Riedel;  Hatakeyama;  and  Levene  &  Rolf  obtained 
linolic  and  arachidonic  acids.  In  another  paper  Levene  &  Rolf 
showed  that  the  lecithin,  carefully  freed  from  kephalin,  contained 
only  palmitic,  stearic,  and  oleic  acids :  saturated  and  unsaturated 
molecules  being  present  in  equal  proportions.  Again,  Stephenson  in 
1 9 1 2  found  an  acid  in  the  phosphatide  fraction  from  egg-yolk,  which 
had  20  carbon  atoms  and  6  or  8  unsaturated  linkages.  Although 
the  proportion  of  unsaturated  acids  in  egg-yolk  is  generally  agreed 
to  be  small,  yet  it  may  be  of  importance  for  the  young  embryo  if 
it  passes  through  a  period  in  the  early  developmental  stages  before 
it  has  the  power  of  desaturating  the  ordinary  fatty  acids.  Evidence 
which  suggests  this  will  be  presented  later  (Section  1 1  •  i ) . 

The  nitrogenous  radicle  in  ovolecithin  is  largely  choline,  but 
difficulty  was  at  first  experienced  in  obtaining  a  theoretical  yield 
on  hydrolysis;  thus  Moruzzi  got  only  77  per  cent,  in  1908  and 
McLean  only  65  per  cent,  in  1909.  This  was  accounted  for,  however, 
when  it  was  found  that  amino-ethyl  alcohol  was  also  present.  The 
two  bases  together  make  up  all  the  nitrogen  in  the  molecule.  Erlandsen 
was  the  first  to  question  the  view  that  lecithin  alone  accounted  for 
the  phosphatide  fraction,  but  he  was  not  himself  able  to  isolate  any- 
thing else.  Later  workers  (Levene  &  West  and  Stern  &  Thierfelder), 
however,  found  that  kephalin  is  also  present  in  yolk,  and  it  would 
probably  be  in  the  kephalin  molecule  that  the  unsaturated  fatty  acids 
would  be  present.  Analyses  of  kephalin  from  the  yolks  of  fowls  are 
given  in  Table  10  ^.  McLean  in  1909  isolated  from  egg-yolk  a  third 
phosphatide  which  resembled  cuorin,  but  it  is  very  doubtful  whether 
this  was  a  true  chemical  individual.  Sphingomyelin  has  also  been 
found  in  egg-yolk  by  Levene  (191 6),  and  lignoceric  as  well  as  hydroxy- 
stearic  acid  was  present  in  it. 

All  these  substances  exist  in  the  yolk  in  close  association  with 
the  proteins.    Hoppe-Seyler  it  was  who  first  observed  that,  after 

296  THE   UNFERTILISED   EGG  [pt.  iii 

prolonged  extraction  of  the  yolk  with  ether,  a  considerable  proportion 
of  the  phosphatides  still  remained  behind,  and  could  be  extracted 
with  alcohol.  It  was  thought  for  a  long  time  that  the  phosphatides 
and  the  vitellin  were  in  chemical  combination  which  was  broken 
by  the  alcohol,  but  since  the  paper  of  Fischer  &  Hooker  in  1 9 1 6  the 
general  opinion  has  been  that  this  combination  is  only  physical. 
Stern  &  Thierfelder  isolated  traces  of  the  cerebrosides,  phrenosin  and 
kerasin,  from  egg-yolk  in  1907. 

The  neutral  fats  and  the  lipoids  of  the  yolk  are  variously  affected 
by  the  nature  of  the  fats  in  the  food  of  the  fowl.  Henriques  &  Hansen, 
who  were  the  first  to  investigate  this  subject,  found  that,  if  food  con- 
taining very  unsaturated  acids  was  fed  to  the  laying  hens,  the  neutral 
fats  in  the  eggs  were  affected,  but  not  the  fatty  acid  components  of 
the  lecithin.  Their  figures  are  shown  in  Table  22.  When  the  food 
consisted  of  barley,  pea  or  rice,  the  iodine  number  of  the  neutral 
fats  in  the  egg  varied  round  about  77,  but  hemp  or  linseed  sent  it 
up  to  about  no,  although  no  matter  what  the  food  was  the  iodine 
number  of  the  fatty  acids  in  the  phosphatide  fraction  remained  con- 
stant at  75  or  so.  Henriques  &  Hansen  also  found  that  the  iodine 
number  of  the  fluid  fatty  acids  of  the  neutral  fat  was  normally  107-5, 
and  that  the  fluid  and  solid  fatty  acids  of  the  phosphatide  fraction 
were  151-3  and  98-9  respectively.  The  former  accounted  for  64-3  per 
cent,  of  the  lecithin  fatty  acids.  The  experiments  of  Henriques  & 
Hansen  have  been  repeated  and  confirmed  by  Belin  and  by  Terroine 
&  Belin.  The  last-named  workers,  together  with  McCollum,  Halpin 
&  Drescher,  some  years  later  reported  that  the  lecithin  fatty  acids 
would  vary,  as  well  as  the  neutral  fatty  acids,  with  the  diet  of  the 
hen.  Their  figures,  which  are  given  in  Table  22,  certainly  show  a 
variation  in  the  iodine  numbers  of  both  fractions.  All  these  workers 
recognised  the  presence  of  unsaturated  acids  in  the  yolk  fat,  and 
Henriques  and  Hansen's  figures  came  between  the  theoretical  values 
for  oleic  and  linolic  acids. 

Work  was  continued  along  these  lines  by  McGlure  &  Carr.  Using 
pigeons,  they  found  that  the  fat  content  of  the  eggs  could  only  be 
altered  slightly  by  feeding  rations  high  and  low  in  fat. 

%  fat  in  the  eggs 
Cocoanut  fat  ...         ...  ...  4-0 

Beef  tallow    ...  ...  ...  ...  6-75 

Average  of  all  fat  diets        ...  ...  4-96 

Average  of  all  non-fat  diets  ...  4-81 


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[PT.  Ill 

Again,  during  the  fat  feeding,  tiie  saponification  value  of  the  egg- 
fat  was  176  (166-190)  and  during  the  rest  of  the  time  173.  The  iodine 
value  was  in  the  former  case  70-5  and  in  the  latter  70-8. 

Table  24.   Lipoid  in  egg-yolk. 




/o                        /o 
Wet  weight   Dry  weight 
























Glikin' s  figures. 


P,05  in       Lecithin 




%  of            in  % 



%  dry 

fatty           of  fatty 




acids            acids 


Pigeon  (yolk) 



3- 16             35-73 




3-88             38-42 


Turtledove  (yolk) 



4-10             46-65 


Starling  (whole  egg)  ... 


5-67             64-44 


Hen  (yolk)       



—                 — 


Cat     ... 

Lecithin  in  %  dry 
weight  at  birth  or  hatching 

Some  suggestive  investigations  on  the  biological  significance  of 
ovolecithin  were  made  b-y  Glikin  in  1 908,  whose  figures  are  shown  in 
Table  24.  Choosing  the  pigeon  as  a  typically  nidicolous  bird,  and 
the  hen  as  a  typically  nidifugous  one,  he  was  able  to  show,  using  a 
variety  of  extraction  methods,  that  the  yolk  of  the  former  was  con- 
siderably richer  in  lecithin  than  the  latter,  the  former  containing 
about  29  per  cent,  dry  weight,  and  the  latter  about  17.  The  further 
but  rather  fragmentary  observations  which  he  made  on  the  starling 
and  the  turtledove  confirmed  this  relationship.  It  is  interesting  that 
Tso  informs  us  that  certain  small  Chinese  breeds  of  hen  produce  very 
small  eggs  (scarcely  40  gm.)  and  that  these  contain  a  much  higher  per- 
centage of  lipoids  than  ordinary  eggs  though  an  equivalent  percentage 
of  protein.  He  concluded  that  lecithin,  one  of  the  most  essential 
yolk-constituents,  was  specially  concentrated  in  nidicolous  yolks  and 


was  associated  with  the  property  of  early  hatching  or  birth.  Thus 
he  compared  the  thrush  (nidicolous)  with  the  guinea-pig,  which  is 
born  almost  ready  to  eat  green  food  and  hardly  passes  through  a 
lactation  stage;  in  the  body  of  the  former  8  gm.  per  cent,  lecithin  dry 
weight  was  found,  in  the  latter  only  4.  The  new-born  cat  and  rabbit 
occupied  intermediate  positions.  It  is  interesting  to  note  that  Glikin's 
figures  bear  out  those  of  Tarchanov  on  the  question  of  water-content 
of  yolks  from  the  two  types  of  birds. 

Tornani  affirmed  in  1909  that  a  difference  in  lecithin-content  was 
observable  between  fertilised  and  unfertilised  eggs.  But  as  he  gave 
no  figures  in  support  of  his  contention,  it  has  not  been  treated  with 
much  respect  by  subsequent  workers. 

The  carbohydrate  of  the  yolk  has  been  the  subject  of  only  a  very 
few  researches  compared  with  that  of  the  white.  The  figures  which 
have  been  obtained  are  shown  in  Table  16,  and  it  will  be  seen  that 
in  no  case  has  the  total  carbohydrate  been  estimated,  and  only 
in  one  case  the  glycogen.  After  Claude  Bernard's  isolation  of  gly- 
cogen from  the  yolk,  a  persistent  belief  grew  up  that  considerable 
amounts  of  this  substance  were  present  there ;  this  was  apparently 
based  on  the  description  by  Dareste  in  1879  of  "amyloid  bodies"  in 
the  yolk  which  gave  microchemically  a  strong  blue  colour  with 
iodine.  Dastre  immediately  pointed  out  that  the  occurrence  of  starch 
there  was  highly  improbable,  and  that  if  any  glycogen  was  there  it 
should  give  a  wine-red  colour;  he  himself,  however,  could  find 
neither.  But  he  did  not  succeed  in  suppressing  the  rumour,  for 
Virchow,  and  later  Schenk,  supported  Dareste,  though  nothing  has 
been  heard  of  this  yolk-constituent  since  1897,  and  Sakuragi's 
analysis  revealed  the  presence  of  only  2-2  mgm.  per  cent,  of  glycogen. 
Bierry,  Hazard  &  Ranc  asserted  in  191 2  that  they  could  obtain  a 
great  increase  of  carbohydrate  after  hydrolysing  the  yolk  with 
hydrofluoric  acid  under  pressure,  but  this  would  not  imply,  as  they 
seemed  to  think,  that  glycogen  was  present,  for  all  kinds  of  other 
compounds  such  as  proteins  (Gross'  protein  for  instance)  might  yield 
glucosamine  under  such  treatment.  They  identified  glucosamine  in 
the  hydrolysate.  On  the  other  hand,  Diamare,  who  hydrolysed  with 
acetic  acid,  could  only  obtain  faint  traces  of  combined  glucose  in 
the  yolk.  He  dialysed  both  white  and  yolk,  and  in  both  cases  was 
able  to  estimate  the  free  sugar,  but  in  the  case  of  the  yolk  very  little 
combined  glucose  seemed  to  be  present.    Further  studies  on  this 

300  THE   UNFERTILISED   EGG  [pt.  iii 

subject  should  be  undertaken,  for  the  methods  of  Diamare  and  Bierry 
ahke  were  of  questionable  reliability.  Diamare,  however,  went  rather 
further  into  the  matter  than  other  investigators,  and,  thinking  that 
the  yolk  glucose  might  only  be  present  there  owing  to  an  inflow  from 
the  white,  examined  the  ovarian  eggs,  in  which  he  found  glucose  in 
much  the  same  proportion  as  in  the  yolks  of  laid  eggs.  He  does  not 
state  whether  the  ovarian  eggs  were  yellow  or  white,  and,  as  he 
frequently  gives  his  results  in  the  form  of  grams  of  glucose  without 
mentioning  the  weight  of  the  fresh  material,  it  is  impossible  to  calcu- 
late the  percentage  (see  also  Tillmans  &  Philippi) . 

We  have  already  seen  that  cholesterol  was  identified  in  the  yolk 
of  the  hen's  egg  by  very  early  workers  such  as  Gobley.  In  1908 
Menozzi  and  in  191 5  Berg  &  Angerhausen  sho\ved  that  egg  cholesterol 
was  identical  with  that  from  milk  and  bile.  It  is  certainly  present 
in  the  unincubated  yolk  both  free  and  in  esterified  form  with  fatty 
acids.  Serono  and  Palozzi  investigated  a  substance  from  egg-yolk  in 
191 1  which  they  called  "lutein"  but  which  turned  out  to  be  nothing 
but  a  mixture  of  cholesterol  esters.  Other  investigators  have  estimated 
the  amount  of  free  and  combined  cholesterol  in  the  unincubated  egg, 
and  their  figures  are  given  in  Table  25. 

Table  25.    Cholesterol-content  of  hen^s  egg. 


per  whole  egg 

Investigator  and  date 

Parke  (1866)        

Mendel  &  Leavenworth  (1908) 
Mueller  (1915)    ... 
Ellis  &  Gardner  (1909)... 
Thannhauser  &  Schaber  (1923) 

Cappenberg  (1909)         

Dam  (1929)         

Schonheimer  (1929)       

Cholesterol      Cholesterol 
(free)                esters 

378                     - 
215-9                 24-2 
489                     - 
173                   54-2 

296                    — 
337                     — 



Free  in  % 
of  total 





Many  Other  substances  have  been  found  to  be  present  in  the  egg  at  the 
beginning  of  development,  e.g.  choline,  alcohol,  creatine,  creatinine, 
inositogen,  lactic  acid,  plasmalogen  (Stepp,  Feulgen  &  Voit,  1927), 
etc.  These  will  be  mentioned  as  occasion  arises  during  the  succeeding 
sections  of  the  book.  Allantoin  is  not  present  (Ackroyd). 

The  yolk  of  the  hen's  egg  also  contains  vitamines,  pigments,  and 
a  variety  of  enzymes,  but  these  will  be  dealt  with  under  their  respec- 
tive sections.    As  Langworthy  has  shown,  it  may  also  contain  very 


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302  THE    UNFERTILISED   EGG   AS   A  [pt.  hi 

various  substances  derived  from  the  diet  of  the  hen,  and  these,  if 
they  are  odorous  or  possess  taste  may  very  easily  betray  their  presence 
(e.g.  the  Swedish  "Schareneier"  described  by  Hansson).  Table  23 
gives  the  figures  which  are  available  for  the  nitrogen  and  Table  26 
for  the  phosphorus  distribution.  These  summaries  bear  out  on  a 
detailed  basis  what  has  already  been  said. 

I -10.    The  Ash  of  the  Avian  Egg 

The  ash  of  the  yolk  and  the  white  of  the  hen's  egg  has  been  in- 
vestigated by  several  workers,  and  a  study  of  it  reveals  certain  inter- 
esting features.  If  Table  27  be  examined,  it  will  be  seen  that,  in  the 
yolk  as  well  as  the  white,  potassium  has  almost  invariably  been  found 
to  be  present  in  greater  amount  than  sodium.  This  is  one  of  the 
characteristics  of  the  egg-cell,  as  will  be  seen  later  when  the  eggs  of 
other  animals  are  considered.  The  yolk  is  also  marked  by  the  very 
high  percentage  of  phosphorus,  most  of  which  is,  in  accordance  with 
other  evidence,  in  organic  combination.  The  calcium  is  also  mainly 
in  the  yolk,  as  is  the  iron,  but  not  the  magnesium.  If  now  the  amounts 
of  metallic  and  acidic  ion  be  calculated  out  in  millimols  and  milli- 
equivalents  per  cent,  wet  weight,  it  is  found  that  in  both  yolk  and 
white  there  is  an  uneven  balance,  but  while  in  the  former  case  there 
is  much  more  anion  than  cation  (anion/cation  ratio  above  unity),  in 
the  latter  case  the  exact  reverse  holds,  and  the  anion/cation  ratio  is 
somewhat  below  unity,  about  0-55.  In  the  white,  therefore,  some  of 
the  potassium  and  sodium  must  be  combined  with  the  proteins,  as 
ovoalbumenates,  etc.*  However,  the  excess  of  cation  over  anion  in 
the  white  is  not  so  considerable  as  the  excess  of  anion  over  cation 
in  the  yolk,  and,  bearing  in  mind  also  the  much  higher  percentage 
of  solid  in  the  yolk  than  in  the  white,  it  would  be  expected  that  the 
anion/cation  ratio  of  the  whole  egg  would  be  greater  than  unity, 
and  would  approach  that  of  the  yolk.  The  facts  show  that  this  is, 
indeed,  the  case,  for  the  average  anion/cation  ratio  calculated  from 
the  results  of  all  observers  for  the  whole  egg  is  2-3,  as  against  2-8 
for  the  yolk  alone  and  0-54  for  the  white  alone.  This  was  first  noted 
by  Garpiaux.   Forbes,  Beegle  &  Mensching  expressed  it  simply  thus : 

Cubic  centimetres  normal  solution 
per  1 00  gm.  dry  weight  egg 
Total  acid     ...  ...  ...  120-28 

Total  base     ...  ...  ...  39*42 

Excess  acid  over  base      ...  ...  8o'86 

*   In  both  white  and  yolk,  of  course,  the  inorganic  ash  is  basic. 

Hen  ... 


Table  27.    Aili  of  the  avian 


%  of  total  ash 








PO,        c 








79-8          - 








79-1          — 








Bi-2        15-2 

Mgm./loo  gm.  wet  weight 

K  Na         Mg  Ca 

2-59        2-72       0-75        3-28 

)-33        048      0-79         3-5 

Fe        SO,       PO, 

.,.„.        .     ,  Total  cation  Total  anion 

Millicquivalents  . '■ ^  , * ^    Anion/ 

K          Na         Mg         Ca          Fe  SO,  PO.  CI  mols     equiv.  mob     equiv.     ratio             Investigator  and  date 

3          —         2-59       2-72        1-50       6-56         —  —  30-9  —  9-34      ,j.j7  ,0-3       jo-j       231      Polcck  (1850) 

y          -         3-33        0-48        1-58        7-u           -  -  35-7  -  8-t        ,2-39  ,,-9       jj.7        ,.-88     Rose  (1850) 

65       738        4-5         0-9.        1-66        7-0           —  _  34-95  7.38  9-79      /.,■„  ,9.03      ^.^j      3.00     Bialascewicz  (1926) 

3-32      50-3         S'll"       173        204 

93  —  3-8       604         ]o8  443        8-8        0-34 

004        636       302        443 

4-6  —         o-o8       19-08 

S-j/        9-42      s2-;a 

Plimmer  &  Lowtidnt  (1927) 
Vaughan  &  Bills  (t878) 
Delezeime  &  Foumeau  (1918) 

Carpiaux  {1908) 
Buckner  &  Martin  ( 


)125  17-5  273  fo 

)I30  15-4  23-8  Trace 

3-590  23-55  ao-7  0-96 

0-720  a7-tiG  i'2-i  2-7 

0-634        —          —  24-B       25 

o-Goo  22-1  20-63  1-41        I 

















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0-65         0-40 

3-56        5-3 
5-11        3-8 









7-17      77-0^      0-C25  Champion  &  Pellet  (1876) 

(not  very  reliable) 
7-77      17-84      0-G29 


0-9       4-4         9-39       s-s8 

S-72  0-58  Poleck  (1850) 

3-51        4-12  035  Rose(iB5o) 

-  -  -  Voit(,877) 
4-82       ssf  c-55  lljin  (1917) 

—  —  —  Prout  (1822) 

—  —  —  —  4-25'      — 

523       4-l'8       3-79        1-24       8-72        - 
345      '0-9  '-"8       2-2        13-62        — 

129-a        52-5 

85-5  4-25 
Go- 16  3-6 
84-6  — 

64-7       1-8 
48-4       3-7 

.■58  6-6 
!-48  9-0 
2-4         9-6 


Average  ...    0-54 


-  -        139-8 

Straub  &  Hoogcrduyn  (1929) 

Poleck  (1850) 

Rose  (1850) 

Voit  (1877) 

Carpiaux  (1903) 

lljin  (1917) 

Prout  (1822) 

Straub  &  Hoogerduyn  (1929) 

*Kreis  &  Studinger. 


This  is  probably  the  most  interesting  consideration  that  emerges 
from  Table  27,  but  it  may  also  be  noted  that  the  ash-content  of  the 
white  is  just  about  half  that  of  the  yolk,  a  relation  which  would 
practically  be  reduced  to  equality  if  the  phosphorus  in  the  yolk  was 
not  taken  into  account. 

The  presence  of  certain  chemical  elements  of  lesser  biological  im- 
portance has  been  announced  from  time  to  time  in  a  group  of  papers 
which  have  some  interest,  although  it  is  difficult  to  see,  as  yet,  what 
their  importance  is  for  the  development  of  the  embryo.  Fluorine  has 
been  estimated  by  Tammann  and  by  Nickles,  copper  by  Dhere, 
boron  by  Bertrand  &  Agulhon,  manganese  by  Bertrand  &  Medigre- 
ceanu,  iodine  by  Bonnanni  and  by  von  Fellenberg,  lead  by  Bishop. 

These  elements  appear  to  be  normal  constituents  of  the  egg.  The 
iron-content  can  be  artificially  increased  by  feeding  iron-rich  rations 
to  the  hen,  and  iodine  can  also  be  introduced  into  the  egg  in  this  way, 
as  has  been  done  by  Bonnanni,  Kreis  and  others,  but  Hofmann  found 
that  though  iron  and  iodine  would  enter  the  egg  thus,  it  was  impossible 
to  get  copper  to  do  so.  In  just  the  same  way  Ricci  found  it  difficult 
if  not  impossible  to  get  As  or  Hg  into  the  hen's  egg  by  feeding  sub- 
toxic  doses  to  the  hen.  The  normal  copper-content  of  the  hen's  egg 
cannot  be  varied  like  its  iron-content.  The  importance  of  iron  in 
the  formation  of  haemoglobin  is  obvious,  and  the  little  that  is 
known  about  this  process  will  be  discussed  in  the  section  on  pigments 
in  the  embryo.  Wassermann  made  a  histochemical  examination 
of  the  egg-yolk  and  vitelline  membrane  for  iron,  and  found  a 
relationship  between  the  embryonic  blood-islands  and  the  iron  of 
the  yolk. 

Some  of  the  other  data  in  Table  28  call  for  comment,  Tammann's 
1-13  mgm.  per  cent,  fluorine  in  the  fresh  yolk  works  out  at  a  quantity 
of  0-2  mgm.  per  egg,  and,  as  Zaleski  found  0-23  per  cent,  fluorine 
in  the  bones  of  the  chick  at  hatching,  o-o8  mgm.  fluorine  would  be 
required  in  the  egg  at  the  beginning,  or  less  than  half  of  what  is 
actually  there.  Zaleski's  figure,  however,  is  old,  and  may  be  too  low. 
It  would  appear,  on  the  whole,  as  if  the  greater  part  of  the  fluorine, 
iodine,  copper,  zinc,  lead,  aluminium,  silicon  and  manganese  is 
localised  in  the  yolk,  and  the  greater  part  of  the  boron  and  arsenic  in 
the  white.  In  view  of  the  importance  which  we  now  attribute  to  these 
less  common  elements  as  catalysts  in  living  tissues,  this  distribution 
may  be  found  to  have  considerable  significance. 




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3o6  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

The  figures  which  have  been  obtained  by  those  investigators 
who  have  examined  the  iron-content  of  eggs  are  seen  in  Table  29. 
All  found  a  great  deal  more  iron  in  the  yolk  than  in  the  white, 
as  might  have  been  expected  from  the  earlier  micro-chemical 
researches  of  Tirmann  and  Kobert.  This  kind  of  work  had  been 
originated  by  Schmiechovski,  and  was  continued  later  by  Wasser- 
mann  in  the  interesting  paper  already  referred  to.  Schmiechovski 
found  iron  histochemically  throughout  the  yolk,  but  considered  that, 
in  the  white  or  milky  yolk,  it  was  confined  to  the  megaspheres. 

Table  29*   Iron  in  hen's  eggs. 

Italic  figures  indicate  dry  weight  data. 
FcaOs  gm.  %  wet  weight 

Without  iron-rich  diet  With  iron-rich  diet 

, ' ^  r  ^ ^ 

Egg-white  Egg-white 

Egg-                       plus  Egg-                       plus 

white      Yolk       yolk       Shell  white      Yolk       yolk       Shell     Investigator  and  date 

•0024      -0088      -0047       -0272  -0040      'oogs      -0059       -0272   Loges  &  Pingel  (1901) 

—  —        -0046          —  —           —        -0040          —      Kreis  (1900) 
•0057      -026        •0165         —  —           —           —           ^      Lebbin  (1900) 
■03          -05          -03              _____ 

•001 12  -00995  '00425  —           —  —           —  —  Hartung  (Mar.  1902) 

•00087  -01106  -00451  —           —  —           —  —             ,,         (May  1902) 

—  —           —  —  -00208  -01621  -00729  —             ,,         (June  1902) 
Trace  -0108         —  —           —  —           —  —  Bunge  (1892) 

—  -0121      -0018  —  —        '0175      -0032  —      Hofmann  (1901) 

—  -;r       -0057  —  —  —  —  —      Boussingault  (1850) 

—  -063         -og§  —  —  —  —  —      Leveque  &  von 

Tschermak  (191 3) 
None     'OI43         —  —        None       '0143         —  —      Elvehjem,  Kemmerer, 

Hart,  &  Halpin  (1929) 

Wassermann,  using  both  the  ammonium  sulphide  and  the  Berlin 
blue  methods,  decided  that  it  was  present  in  both  kinds  of  yolk, 
but  that  it  was  not  confined  to  those  special  elements  in  the  white 
part.  In  fact,  it  was  very  much  more  abundant  in  the  white  than 
in  the  yellow  part.  This  finding  has  never  been  corroborated  by 
chemical  analysis,  but,  if  it  is,  it  will  have  considerable  importance, 
in  view  of  the  time  at  which  haemoglobin  is  most  vigorously  manu- 
factured by  the  embryo.  For  a  further  discussion  of  these  questions 
see  the  section  on  pigments. 

i-ii.    General  Characteristics  of  Non- Avian  Eggs 

With  this  we  may  conclude  the  discussion  of  what  is  known 
about    the    typically    terrestrial    egg,    that    of    the    bird.      Now 


aquatic  species  far  outnumber  the  terrestrial  ones;  as  Spenser 
put  it: 

O !  What  an  endlesse  Worke  have  I  in  hand 

To  count  the  sea's  abundant  progeny, 
Whose  fruitfull  seede  farre  passeth  those  on  land, 

And  also  those  which  wonne  in  th'  azure  sky: 
For  much  more  eath  to  tell  the  starres  on  hy, 

Albe  they  endlesse  seeme  in  estimation, 
Than  to  recount  the  sea's  posterity. 

So  fertile  be  the  flouds  in  generation, 

So  huge  their  numbers,  and  so  numberlesse  their  nation. 

It  might  therefore  be  supposed  that  a  much  greater  space  would 
have  to  be  devoted  to  their  eggs  than  what  has  already  been  taken 
up,  but  this  is  not  the  case,  for  the  bird's  egg  has  been  so  convenient 
a  material  for  research  that  the  knowledge  we  have  of  it  outweighs 
that  of  the  eggs  of  all  other  animals  put  together.  Indeed,  the  data 
about  the  eggs  of  other  groups  are  very  fragmentary,  so  that  much 
caution  has  to  be  used  in  making  comparisons,  and  general  relation- 
ships are  much  more  difficult  to  enunciate.  Van  Beneden's  classical 
memoir  may  be  recommended  as  an  account  of  the  morphology  of 
the  eggs  which  are  to  be  mentioned,  and  it  is  hardly  necessary  to 
refer  to  Balfour's  book  on  comparative  embryology. 

If  Table  30  is  examined,  and  compared  with  Table  2,  it  will  at 
once  be  seen  that  the  percentage  composition  of  eggs  of  other  classes 
of  animals  differs  markedly  and  in  very  definite  ways  from  the  egg 
of  the  hen.  The  case  of  reptiles  may  first  be  taken,  as  being  less  remote 
than  others.  The  reptilian  egg  seems  to  be  distinctly  drier  than  that 
of  the  bird,  by  about  20  per  cent.,  and  much  more  variable  in  its 
fat/protein  ratio.  For,  while  in  all  birds'  eggs  that  have  been  in- 
vestigated, the  amount  of  protein,  whether  related  to  dry  or  to  wet 
weight,  is  about  the  same  as  that  of  fat,  the  reptilian  egg  shows  big 
variations  from  this  rule.  In  the  eggs  of  the  tortoise  and  lizard,  for 
example,  there  is  twice  as  much  protein  as  fat,  while  in  those  of  the 
grass-snake,  studied  by  Galimard,  there  is  three  times  as  much  fat 
as  protein.  This  fact  will  be  mentioned  again  later  (see  p.  313). 
Considerably  more  is  known  however  about  those  of  amphibia, 
which  have  also  been  found  to  contain  a  great  deal  more  protein 
than  fat.  Thus,  instead  of  the  40  per  cent,  protein  and  the  40  per 
cent,  fat  which  make  up  the  dry  substance  of  the  hen's  egg,  Faure- 

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312  THE   UNFERTILISED   EGG   AS   A  [pt.  m 

Fremiet  &  Dragoiu  found  the  dry  material  of  the  egg  of  the  frog  to 
consist  of  60  per  cent,  protein  and  only  14  per  cent.  fat.  And  this  has 
been  the  experience  of  all  those  who  have  analysed  amphibian  eggs. 
Next  to  the  hen's  egg,  the  eggs  of  fishes  have  probably  received 
the  most  attention.  The  recorded  analytical  figures  for  fish  eggs  are 
often  deceptive,  for  many  analyses  have  been  made  of  salted  fish 
roes  and  egg-preparations  such  as  caviar,  but  the  greatest  care  has 
been  taken  not  to  include  in  Table  30  results  which  might  have  been 
vitiated  in  that  way.  The  question  is  complicated  by  the  fact  that 
analyses  of  the  purified  constituent  egg-substances  prepared  from 
preserved  material  may  well  be  admitted  into  consideration,  for, 
except  in  certain  cases,  they  would  probably  not  undergo  much 
change  during  the  process  of  preservation.  As  in  the  case  of  reptiles 
and  amphibia,  the  fish  egg  is  characterised  by  its  predominance  of 
proteins  as  the  food  of  the  growing  embryo.  It  should  be  remembered 
that,  in  all  these  comparisons,  the  yolk  of  the  hen's  egg  is  a  more 
proper  standard  of  reference  than  the  whole  egg-contents,  in  which 
case  the  differences  become  even  more  remarkable.  This  generalisa- 
tion appears  at  all  points;  thus,  the  brook-trout,  a  fresh-water  fish, 
has  30  per  cent,  of  protein  and  only  9  per  cent,  of  fat,  and  the  herring 
has  26  per  cent,  as  against  3  per  cent.  In  Table  31  the  protein/fat 
ratios  are  collected  together,  and  the  difference  emerges  there  with 
great  clearness.  Though  it  is  obvious  that  fishes  vary  considerably 
among  themselves  as  to  the  fat-content  of  their  eggs,  yet  all  of 
them  have  more  protein  than  fat.  The  only  fishes  in  Table  31 
which  come  near  to  being  exceptions  to  this  rule  are  the  sturgeon 
and  the  dogfish,  both  of  which  have  an  unusually  high  amount  of 
fat  in  their  eggs  (a  fact  which  accounts  for  the  superiority  of  Russian 
caviar  over  other  varieties,  for  the  former  is  made  chiefly  from  the 
eggs  of  sturgeon) .  Besides  this  general  difference  between  the  egg  of 
the  bird  and  that  of  the  fish,  there  are  many  others,  but  they  concern 
the  chemistry  of  the  individual  components  rather  than  the  rough 
constitution  of  the  egg  as  a  whole,  and  will,  therefore,  be  dealt  with 
later  on.  If  Table  31  be  further  studied,  it  will  be  seen  that,  as  far  as 
can  be  known  at  present  from  the  few  analyses  of  crustacean  and 
cephalopod  eggs,  the  superior  proportion  of  protein  over  fat  holds 
good  there  also.  Curiously  enough,  the  only  analysis  we  have  for 
a  gastropod  egg  gives  a  picture  more  resembling  the  egg  of  the  hen, 
comparatively  equal  amounts  of  fat  and  protein  being  present. 

SECT.    l] 



The  position  of  affairs  may  perhaps  be  summarised  by  saying  that 
it  is  only  the  birds  which  have  been  successful  in  producing  an  egg 
really  well  stocked  with  fat,  though  the  reptiles  clearly  show  an 
approximation  to  this  achievement.  Does  this  mean  that  the  storage 
of  fat  in  the  egg  is  particularly  associated  with  terrestrial  embryos? 
The  facts  and  arguments  to  be  brought  forward  in  later  chapters  (see 
Sections  7-7,  9-15  and  1 1-8)  make  this  hypothesis  a  very  likely  one,  but, 
as  Table  31  shows,  the  silkworm  (the  only  representative  of  terrestrial 

Table  31.   Protein/ fat  ratio  in  various  eggs. 




Hen  (yolk) 
„    (whole  egg) 







































arthropods)  does  not  seem  to  have  succeeded  in  storing  fat  in  its 
egg  to  any  great  extent.  It  might,  of  course,  be  argued  that  this  was 
one  of  the  factors  which  prevented  the  insects  attaining  any  con- 
siderable size  and  rivaling  reptiles  and  mammals  for  the  possession 
of  the  land.  The  mammals  gave  up  the  heavy  fat  storage  in  the  egg 
when  they  invented  viviparity  and  the  fully  developed  placenta.    In 

314  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

this  connection  the  monotreme  egg  would  be  a  chemical  study  of 
great  interest,  and  it  is  characteristic  of  the  exasperating  fragmenta- 
tion of  this  field  of  work  that  all  we  know  about  the  monotreme  egg 
is  that  its  membrane  seems  to  have  the  properties  of  a  keratin.  The 
suggestion  that  the  metabolism  of  the  fowl,  operating  on  a  con- 
tinuously high  level  of  energy  turnover,  would  naturally  tend  to  fill 
up  the  eggs  with  fat,  and  is  associated  with  the  well-known  higher 
temperature  of  the  avian  body  (Wetmore)  may  not  be  without  value, 
but  any  special  emphasis  on  fat  metabolism  in  adult  birds  is  precluded 
by  the  statements  in  Schulz's  review. 

It  is  very  significant  that  as  animals  became  more  complicated  and 
more  adaptable  to  varied  surroundings,  higher,  in  fact,  in  the  taxo- 
nomic  scale,  they  loaded  their  eggs  to  a  greater  extent  with  yolk.  Since 
the  extra  material  was  usually  fatty  acids,  this  process  appears 
strikingly  in  Table  31 .  The  effects  of  the  yolk  have  long  been  familiar 
to  embryologists,  and  have  been  best  described,  perhaps,  in  a  passage 
by  Milnes-Marshall.  "The  immediate  effect  of  a  large  amount  of 
yolk",  he  said,  "is  to  retard  mechanically  the  processes  of  develop- 
ment, but  the  ultimate  result  is  to  shorten  them.  This  paradox  is 
readily  explained.  A  small  egg,  such  as  that  of  Amphioxus,  starts  its 
development  rapidly,  and  in  about  eighteen  hours  gives  rise  to  a 
free-swimming  larva,  capable  of  independent  existence,  with  a 
digestive  cavity  and  a  nervous  system  already  formed ;  while  a  large 
egg  such  as  that  of  the  hen,  hampered  by  the  great  mass  of  yolk 
by  which  it  is  distended,  has,  in  the  same  time,  made  very  little 
progress.  From  this  time  onwards,  however,  other  considerations 
begin  to  tell.  Amphioxus  has  been  able  to  make  this  rapid  start  owing 
to  its  relative  freedom  from  yolk,  but  now  this  freedom  becomes  a 
retarding  influence,  for  the  larva,  containing  within  itself  but  a  very 
scanty  supply  of  nourishment,  must  devote  much  of  its  energies  to 
hunting  for  and  to  digesting,  its  food,  and  hence  its  further  develop- 
ment will  proceed  more  slowly.  The  chick  embryo  on  the  other  hand 
has  an  abundant  supply  of  food  in  the  egg  itself  and  has  no  occasion, 
therefore,  to  spend  its  time  searching  for  it,  but  can  devote  its  whole 
energies  to  the  further  stages  of  its  development.  Hence,  except  in 
the  earliest  stages,  the  chick  develops  more  rapidly  than  Amphioxus 
and  attains  its  adult  form  in  a  much  shorter  time.  The  tendency  of 
abundant  yolk  to  lead  to  shortening  or  omission  of  the  ancestral 
history,  is  well  known.  The  embryo  of  forms  well  provided  with  yolk 


takes  short  cuts  in  its  development,  and  jumps  from  branch  to  branch 
of  its  genealogical  tree  instead  of  climbing  steadily  upwards.  Thus 
the  little  West  Indian  frog,  Hylodes,  produces  eggs  which  contain  a 
larger  amount  of  yolk  than  those  of  the  ordinary  English  frog.  The 
young  Hylodes  is  consequently  enabled  to  pass  through  the  tadpole 
stage  before  hatching,  and  to  attain  the  form  of  the  frog  before  leaving 
the  c:gg\  the  tadpole  stage  is,  in  fact,  only  imperfectly  recapitulated, 
the  formation  of  gills,  for  instance,  being  entirely  omitted." 

The  more  yolk,  then,  the  longer  the  embryo  can  remain  an  embryo 
before  having  to  face  the  external  world,  and  the  more  preparations 
it  can  make  for  that  event.  It  is  probable  that  this  question  is 
intimately  bound  up  with  the  penetration  of  fresh-water  surroundings 
by  the  originally  marine  forms.  "It  has  long  been  noticed",  said 
Milnes-Marshall,  following  the  classical  exposition  of  Sollas, "  that 
marine  animals  lay  small  eggs  whereas  their  fresh-water  allies 
lay  eggs  of  much  larger  size.  The  eggs  of  the  salmon  or  trout  are 
much  larger  than  those  of  the  cod  or  the  herring,  and  the  crayfish, 
though  only  a  quarter  the  length  of  the  lobster,  lays  eggs  of 
actually  larger  size.  The  larger  size  of  the  eggs  of  the  fresh-water 
forms  appears  to  be  dependent  on  the  nature  of  the  environment 
to  which  they  are  exposed.  Considering  the  geological  instability 
of  the  land  as  compared  with  the  ocean,  there  can  be  no  doubt  that 
the  fresh-water  fauna  is,  speaking  generally,  derived  from  the 
marine  fauna,  and  the  great  problem  with  regard  to  fresh-water  life 
is  to  explain  why  it  is  that  so  many  groups  of  animals  which  flourish 
abundantly  in  the  sea  should  have  failed  to  establish  themselves  in 
fresh  water.  Sponges  and  Coelenterates  abound  in  the  sea,  but  their 
fresh- water  representatives  are  extremely  few  in  number;  Echino- 
derms  are  exclusively  marine ;  there  are  no  fresh-water  Cephalopods, 
no  Ascidians,  and  of  the  smaller  groups  of  Worms,  Molluscs,  and 
Crustacea,  there  are  many  that  do  not  occur  in  fresh  water.  Direct 
experiment  has  shown  that  in  many  cases  this  distribution  is  not  due 
to  the  inability  of  the  adult  animals  to  live  in  fresh  water,  and  the 
real  explanation  appears  to  be  that  the  early  larval  stages  are  unable 
to  establish  themselves  under  such  conditions.  To  establish  itself  in 
fresh  water  permanently  an  animal  must  either  be  fixed,  or  else 
be  strong  enough  to  withstand  and  make  headway  against  the  cur- 
rents of  the  streams  or  rivers  it  inhabits,  for  otherwise  it  will  in  the 
long  run  be  swept  out  to  sea,  and  this  condition  applies  to  larval 

3i6  THE   UNFERTILISED   EGG   AS   A  [pt.  iii 

forms  equally  with  adults.  The  majority  of  marine  invertebrates  leave 
the  egg  as  minute  ciliated  larvae,  which  are  quite  incapable  of  holding 
their  own  in  currents  of  any  strength.  Hence  it  is  only  forms  which 
have  got  rid  of  the  free-swimming  ciliated  larval  stage,  and  which 
leave  the  egg  as  organisms  of  considerable  size  and  strength,  that  can 
establish  themselves  as  fresh-water  animals.  This  is  effected  most 
readily  by  the  acquisition  of  yolk — hence  the  large  size  of  the  eggs  of 
fresh-water  animals — and  is  often  supplemented  by  special  devices." 

Here  is  an  explanation  for  the  well-known  paucity  of  eggs  in  fresh- 
water plankton.  In  certain  cases  it  is  possible  to  induce  an  embryo 
to  skip  the  larval  stage  which  it  should  normally  pass  through.  Thus 
Child  could  abolish  the  free-swimming  larval  stage  in  the  ascidian 
Corella  willmeriana,  simply  by  removing  the  eggs  from  the  parental 
atrial  chamber  {p¥L  j'^.)  to  normal  sea-water  (/>H  8-4). 

Giard  had  also  noticed  the  discrepancy  in  egg-size  between  closely 
related  marine  and  fresh-water  forms,  and  had  classed  it  among  those 
cases  where  like  adults  have  unlike  larvae  ("Poecilogony").  The 
classical  instance  is  perhaps  that  of  the  shrimp  Palaemonetes  varians, 
one  variety  of  which  {microgenitor)  lives  in  the  sea  near  Wimereux 
and  has  eggs  0-5  mm.  diam.  (32 1  per  female)  and  another  of  which 
{macro genitor)  lives  in  fresh  water  at  Naples  and  has  eggs  1-5  mm. 
diam.  (25  per  female).  Giard  has  reviewed  this  subject  in  a  very 
interesting  paper.  "Dans  un  groupe  determine",  he  said  {(Euvres 
diverses,  p.  18),  "la  condensation  embryogenique  va  en  croissant  des 
types  marins  aux  types  d'eau  douce  ou  terrestres." 

The  correlated  proposition,  namely,  that  the  fresh-water  forms 
generally  lay  fewer  eggs  than  the  marine  ones,  is  illustrated  by  the 
following  instances  collected  by  Carpenter: 

No.  of  eggs  laid  per  female  per  annum 


Lamellibranchs  ... 


Marine  form 
Ostrea  edulis            i  ,800,000 

Buccinum  undatum        12,000 

Haddock               9,000,000 
Lobster                         5,000 

Fresh-water  form 
Uniopictorum                          220,000 
Anodonta  cygnea                        18,000 
Average  of  many  snails              100 
Average  of  many  limpets               6 
Ovoviviparous  pond-snails          15 
Brook-trout                                   750 
Crayfish                                         200 

Another  reason  for  the  poverty  of  fresh-water  fauna  was  suggested 
by  von  Martens  who  pointed  out  that  the  fresh-water  climate,  with 
its  periods  of  desiccation  and  freezing,  was  much  more  severe  than 


that  of  the  sea.  But  even  these  two  causes  together  cannot  fully 
account  for  the  phenomenon,  for  there  are  many  cases  of  individual 
species  which  they  will  not  cover;  thus  the  Cephalopods,  which  hatch 
out  as  minute  but  very  active  copies  of  their  parents,  i.e.  which  pass 
their  larval  stage  within  the  egg,  and  which  should  therefore  be 
immune  from  the  disadvantage  described  by  Sollas,  never  penetrated 
into  fresh  water. 

A  third  reason  must  be  added  to  those  of  Sollas  and  of  von  Martens. 
As  will  be  shown  in  Sections  12  and  13  the  marine  invertebrate  embryo 
depends  largely  on  the  salts  of  the  sea  water  for  its  supply  of  ash,  and 
therefore  could  not  be  expected  to  develop  in  a  medium  very  poor 
in  inorganic  matter.  Colonisation  of  the  fresh  water  could  not  occur, 
then,  until  animals  had  begun  to  provide  in  each  egg  sufficient  ash 
to  make  one  finished  embryo.  There  seem  to  be  few  data  concerning 
the  capacity  of  marine  invertebrate  eggs  to  develop  in  fresh  water, 
although  the  adult  animals  have  been  found  often  enough  to  ac- 
custom themselves  to  a  fresh-water  environment  (see  the  instances 
given  in  Semper) .  Many  studies  of  the  effect  of  hypotonic  solutions 
on  marine  embryos  can,  however,  be  called  to  mind,  and  in  all  the 
cases  the  results  are  teratogenic. 

The  fate  of  the  Cephalopods,  it  is  interesting  to  note,  is  explained 
by  this  third  factor,  for  Ranzi  has  demonstrated  the  intake  of  the 
salts  in  the  sea  water  by  the  octopus  egg. 

As  for  the  general  statement  that  animals  can  afford  their  young 
a  better  chance  of  survival  by  providing  them  with  larger  amounts 
of  yolk  and  therefore  a  longer  incubation-period,  there  is  a  striking 
parallel  here  with  the  seeds  of  leguminous  plants  which  are  packed 
with  nourishment.  In  the  Origin  of  Species  (6th  ed.  p.  56),  Darwin 
wrote,  "From  the  strong  growth  of  young  plants  produced  from  such 
seeds  as  peas  and  beans  when  sown  in  the  midst  of  long  grass,  it  may 
be  suspected  that  the  chief  use  of  the  nutriment  in  the  seed  is  to 
favour  the  growth  of  the  seedlings,  whilst  struggling  with  other 
plants  growing  vigorously  all  round". 

It  is  interesting  that  the  birds  show  an  adaptation  exactly  similar  to 
the  poecilogony  of  the  invertebrates  and  fishes.  Tree-nesting  birds  are 
usually  nidicolous,  but  the  defenceless  state  of  the  newly-hatched  squab 
has  brought  it  about  that  ground-nesting  birds  are  usually  nidifugous. 

As  Table  30  shows,  the  composition  of  the  eggs  of  all  animals  other 
than  those  of  the  frog,  the  silkworm,  and  certain  fishes,  is  still,  to 

3i8  THE   UNFERTILISED   EGG   AS   A  [pt.  m 

use  a  phrase  of  William  Harvey's,  "hid  in  obscurity  and  deep  night". 
It  is  as  yet  much  too  early  to  try  to  draw  any  conclusions  from  the 
very  fragmentary  figures  which  are  all  that  we  have  at  our  disposal, 
and  we  may  well  admit  that  one  of  the  most  urgent  needs  of  chemical 
embryology  is  a  much  wider  extension  of  our  knowledge  of  the  static 
chemistry  of  the  egg.  This  is  a  quite  indispensable  preliminary  to  the 
investigation  of  the  metabolism  of  the  embryo  in  the  lesser  known 
forms.  The  attempt  has  already  once  been  made  to  link  up  in  some 
way  the  chemistry  of  the  egg  with  what  is  known  of  the  type  of 
embryonic  development  which  takes  place  in  it.  Wetzel  in  1907 
analysed  the  eggs  of  a  sea-urchin,  a  crab,  a  cephalopod,  and  an 
elasmobranch  fish.  He  pointed  out  that  the  eggs  he  studied 
were  examples  of  varying  richness  in  yolk,  of  total  and  partial, 
equal  and  unequal,  superficial  and  discoidal  cleavage,  as  well  as 
chemical  systems.  Taking  the  egg  of  Strongylocentrotus  lividus  as 
his  first  case,  he  regarded  it  as  typical  of  a  class  of  alecithic 
eggs,  of  a  total  and  equal  cleavage  type,  and  he  drew  attention 
to  the  fact  that  it  was  rich  in  water  and  in  salts,  but  poor  in 
fatty  substances,  in  nitrogen,  and  in  phosphorus.  Similarly,  in  the 
case  of  the  mollusca,  where  there  is  no  very  definite  type  of 
development,  the  egg  of  Sepia  could  not  stand  as  representative  of 
any  wider  class  than  the  cephalopods,  but,  as  far  as  it  went,  it 
showed  that  the  cephalopod  egg  was  rich  in  nitrogen,  poor  in  fat  and 
inorganic  substances,  with  a  moderate  phosphorus  and  water-content. 
The  decapod  Crustacea,  to  which  Maia  squinado  belongs,  have  a 
purely  superficial  type  of  cleavage,  with  no  cell-multiplication  in  that 
part  of  the  egg  which  holds  the  yolk.  Accordingly,  the  egg  possessed 
a  moderate  fat  and  water-content,  a  moderate  ash,  and  much  protein 
and  phosphorus. 

The  mammalian  ovum  is  still  as  unknown  chemically  as  it  was 
when  Wetzel  was  writing,  and  it  may  be  found  to  have  a 
constitution  not  unlike  the  alecithic  echinoderm  eggs.  For  the 
eggs  of  birds  (and  of  reptiles,  which  only  differ  from  them  in 
having  very  little  egg-white)  Wetzel  found  a  low  protein  and 
water-content,  a  high  proportion  of  fat  and  ash,  and  a  large  amount 
of  calcium  and  phosphorus.  Here  cleavage  would  only  take  place 
at  one  isolated  point  on  the  surface  of  the  mass  of  food-material. 
In  the  amphibia,  the  richness  of  yolk,  while  much  more  significant 
than  in  lower  classes,  does  not  reach  the  level  of  birds  and  reptiles. 


and  this  is  duly  reflected  in  the  chemical  composition  by  the  moderate 
water-content,  the  high  proportion  of  protein  which  is  yet  only 
double  that  of  the  fat.  The  case  of  the  dogfish  is  again  different,  for 
there  the  egg  is  rich  in  yolk  and  the  cleavage  is  meroblastic;  thus 
the  water  is  rather  low,  the  fat  rather  high,  the  nitrogen  very  high, 
and  the  ash  and  phosphorus  moderate. 

But  these  conclusions  of  Wetzel's,  interesting  though  they  are,  can- 
not really  be  assessed  until  a  great  deal  more  comparative  work  has 
been  done.  They  must  rather  be  taken  to  represent  the  kind  of  cor- 
relation we  may  hope  for  in  the  future.  However,  one  of  Wetzel's 
generalisations  may  be  accepted,  if  with  some  reserve.  He  pointed 
out  that  the  fat-content  of  eggs  showed  great  variations,  rising  from 
12  per  cent,  of  the  dry  weight  of  the  Sepia  ^gg  to  66  per  cent,  of  the 
dry  weight  of  the  (yolk  of  the)  hen's  tgg.  Again,  the  nitrogen 
gave  very  variable  results,  rising  from  5-3  per  cent,  of  the  dry 
weight  in  the  (yolk  of  the)  hen's  ^gg  to  6-9  per  cent,  in  the  egg 
of  the  grass-snake,  1 2  per  cent,  in  the  egg  of  the  dogfish,  and  even 
in  the  case  of  the  cod  14  per  cent.  On  the  other  hand,  the  phosphorus- 
content  varied  only  between  the  (outside)  limits  of  2  •  i  per  cent,  for 
the  sea-urchin  tgg  and  3-6  per  cent,  for  that  of  the  grass-snake. 
Wetzel,  therefore,  suggested  that  a  distinction  might  be  made,  at  any 
rate,  roughly,  between  those  constituents  of  the  egg  which  may  serve 
as  sources  of  energy  for  the  growing  embryo,  and  those  which  in 
no  circumstances  do  so.  Protein,  fat,  and  carbohydrate  would  come 
in  the  former  class;  phosphorus  (for  nucleoprotein)  and  cholesterol, 
for  example,  would  come  in  the  latter  class.  The  former  would  show 
great  variations  among  eggs  of  different  species,  the  latter  would  not. 
He  thus  supposed  that  one  might  be  able  to  deduce,  as  it  were,  the 
constitution  of  any  given  egg,  if  one  knew  what  substances,  and  in 
what  proportions,  were  used  by  the  embryo  as  combustible  material 
during  its  development,  as  well  as  the  constitution  of  the  newly  born 
or  hatched  organism. 

From  this  standpoint  Wetzel  distinguished  four  types  of  substances 
in  the  unincubated  egg :  ( i )  material  for  the  embryo  to  burn  during 
the  course  of  its  development,  (2)  constituents  of  the  finished  proto- 
plasm of  the  embryo,  (3)  constituents  of  the  finished  embryo,  but 
not  for  incorporation  into  the  protoplasm  itself,  but  into  the  para- 
plasm (in  Le  Breton's  terminology),  (4)  the  protoplasm  of  the  original 
egg-cell.   No  aspect  of  chemical  embryology  needs  attention  more 

320  THE   UNFERTILISED   EGG   AS   A  [pt.  iii 

urgently  than  this,  and  the  correlation  of  chemical  constitution  with 
developmental  type  should  offer  a  most  attractive  field  for  research. 

But  it  is  not  only  correlations  of  this  type  that  lie  hidden  under 
the  enigmatic  character  of  analytical  figures.  The  water-content  of 
the  eggs  may  have  a  powerful  effect  on  the  sex-ratio,  for  King  found 
in  191 2  that  reducing  the  water-content  of  fertilised  frog's  eggs  con- 
siderably lowered  the  proportion  of  males,  while  increasing  it  by 
means  of  treatment  with  dilute  acid  considerably  raised  the  pro- 
portion. A  discussion  of  these  facts  in  relation  to  genetics  as  a  whole 
will  be  found  in  the  review  of  Huxley.  It  is  probable  that  the  effect 
which  delayed  fertilisation  has  upon  the  sex-ratio  is  to  be  explained 
by  difference  in  water-content  of  the  eggs.  Hertwig  was  the  first  to 
observe  this  delayed  fertilisation  phenomenon  in  some  work  which 
he  published  in  1905,  and  since  then  it  has  many  times  been  observed 
not  only  for  amphibia  but  also  for  trout  (Kuschakevitsch;  Huxley; 
Mrsic) .  Riddle  has  suggested  that  the  mammalian  egg  may  be  subject 
to  such  influences  as  it  passes  from  ovary  to  uterus.  He  quotes  van 
der  Stricht's  histological  work  on  the  bat's  egg  during  this  process, 
and  points  out  that  the  swelling  of  the  yolk-granules  would  indicate 
an  absorption  of  water.  The  exact  degree  of  hydration  of  the  mam- 
malian egg  might  thus  conceivably  have  an  effect  on  the  mammalian 

Table  30  has  several  more  important  points  which  have  not,  so 
far,  been  touched  upon.  It  is  interesting  to  follow  in  the  figures  of 
Milroy  the  difference  between  the  fish  eggs  which  float  at  the  surface 
of  the  water  during  their  development  (pelagic  ova),  and  those  which 
sink,  or  rather  float,  at  lower  and  denser  levels  (demersal  ova) — 
the  former  have  a  water-content  of  about  90  per  cent.,  the  latter  of 
about  70  per  cent.  A  knowledge  of  the  chemical  composition  of  fish 
eggs  throws  a  great  deal  of  light  upon  their  distribution  in  the  sea, 
and  so  indirectly  upon  ecological  problems.  Their  fat-content,  for 
example,  has  been  treated  from  this  point  of  view  by  Polimanti,  whose 
work  will  be  discussed  in  the  section  on  the  general  metabolism 
of  the  embryo;  and  the  investigations  of  the  specific  gravity  of  fish 
eggs,  which  are  discussed  in  Section  5,  have  also  an  important 
bearing  upon  these  problems.  Another  point  worth  notice  is  the 
approximately  constant  percentage  of  cholesterol  in  different  eggs, 
nearly  always  about  500  mgm.  per  cent,  of  the  wet  weight,  a  pro- 
portion which,  roughly  speaking,  holds  for  the  egg  of  the  hen  as  well. 


It  would  be  as  well  to  emphasise  the  fact  that  no  principle  of  selec- 
tion has  been  used  in  the  preparation  of  Table  30,  on  the  ground 
that  results  such  as  those  of  Roffo  &  Correa  on  a  Brazilian  gastropod, 
and  McCrudden  on  fresh-water  fishes,  which  seem  obviously  wrong, 
may  not  be  so  at  all.  The  estimation  methods  and  analytical  processes 
which  are  by  general  consent  judged  most  satisfactory  at  the  present 
time  cannot  be  considered  in  any  way  final,  and  to  have  excluded 
certain  results  on  account  of  the  technique  employed  in  obtaining 
them  would  not  have  been  justifiable.  Table  30  does  not,  therefore, 
absolve  investigators  fi'om  the  duty  of  looking  up  the  original  papers 
in  such  cases  as  touch  them  most  closely,  and  forming  an  independent 
judgment,  according  to  the  best  opinion  of  the  time,  on  the  stress 
which  can  be  laid  upon  them.  It  is  needless  to  say  that  I  leave  out 
of  account  all  doubtful  figures  in  the  generalisations  made  here. 

I -12.    Egg-shells  and  Egg-membranes 

Very  little  is  known  about  the  relative  proportions  of  yolk,  white, 
and  shell,  in  the  eggs  of  the  lower  animals,  or  rather,  in  most  cases, 
egg-contents  and  shell  or  surrounding  membrane.  Table  32  gives  a 
few  figures.  The  discrepancy  between  the  results  of  Ford  &  Thorpe, 
on  the  one  hand,  and  Wetzel,  on  the  other,  is  very  strange,  especially 
as  they  both  used  Scyllium  canicula  eggs,  but  it  is  probably  due  to 
insufficiency  of  the  statistical  element.  Ford  &  Thorpe's  proportions 
are  more  likely  to  be  accurate. 

Much  work,  however,  has  been  done  on  the  membranes  and  hard 
coverings  which  invest  the  unincubated  eggs  of  diflferent  kinds  of 
animals.  For  instance,  the  gelatinous  substance  which  surrounds  the 
undeveloped  amphibian  egg  was  examined  chemically  by  Brande 
in  1 810,  who  noticed  that  it  absorbed  water  and  was  not  precipitated 
by  tannin  or  by  strong  acids.  Later  work  has  shown  that  it  consists 
almost  entirely  of  mucoprotein  and  water.  Wetzel's  figures  for  its 
weight  are  shown  in  Table  32.  Giacosa  isolated  mucin  in  a  pure 
state  from  it  in  1882,  and  the  figures  which  he  obtained  for  its  per- 
centage composition  are  shown  in  Table  33.  He  was  able  to  show 
the  presence  of  a  reducing  sugar  on  hydrolysis,  but  he  could 
isolate  nothing  else  from  the  jelly,  and  therefore  concluded  that 
it  was  pure  mucin.  The  presence  of  glucosamine  in  the  muco- 
protein was  afterwards  confirmed  by  Hammarsten,  by  Schulz  & 
Ditthorn  and  by  Wolfenden,  who  confirmed  Giacosa's  finding  that 



[PT.  Ill 

Table  32. 

In  %  of  total  egg-weight 




Carp     ... 
Cod       ... 
Pike      ... 





8-87  (wet) 


Trout   ... 

25-97  (dry) 


Yolk  Investigator  and  date 

—         Konig  &  Grossfeld  (191 3) 

3?  33 

75-3       Ford  &  Thorpe  (1920) 
36-5       Wetzel  (1907) 
—         Tichomirov  (1882) 



Kronfeld  &  Scheminzki  (1926) 
Ranzi  (1930) 

Tomita's  figures. 

Marine  turtle  ( Thalassochelys  cortica) 





m  gm. 








Wetzel's  figures. 

I  Frog  {Rana  temporaria) 

Ovarial  egg  (no  jelly)... 
Egg  with  unswoUen  jelly 
Jelly  alone 
Swollen  jelly     ... 
Water  content  of  ovarial  egg 
„  „  egg  and  jelly 

Empty  dry  jelly 
Dry  egg 

Dry  egg  +  dry  jelly    ... 

Thus  of  dry  weight  egg 


Weight  in  mg. 






Melvin's  figures. 

Shell-weights  of  insects 

Squash-bug  {Anasa  tristis) 
Luna  moth  [Tropoeoa  luna) 
Cecropia  moth  {Sarnia  cecropia)  ... 
Smartweed-borer  {Pyrausta  ainsleii) 





%  of  total 

weight  of  eggs 



it  was  remarkably  resistant  to  putrefaction,  and  studied  the 
effect  of  enzymes  such  as  pepsin  upon  it.  The  resistance  of 
frog  ovomucin  to  putrefaction  was  for  long  a  puzzle  to  bio- 
chemists, but  it  seems  to  be  explained  by  the  unwillingness  of  most 


bacteria  to  grow  on  pure  proteins,  and  as  the  jelly  contains  no 
enzymes  of  an  autolytic  character  no  protein  breakdown  products 
are  formed,  and  consequently  no  bacterial  growth  takes  place.  This 
might  be  considered  a  protection  of  the  developing  embryo  from 
bacterial  attack.  It  is  very  probable,  moreover,  that  the  mucoprotein 
acts  as  a  source  of  nourishment  for  the  young  tadpoles  immediately 
after  hatching,  for  they  invariably  attach  themselves  to  it  after  they 
emerge  from  the  egg-membrane,  and  hang  on  to  it  by  their  oral 
suckers  (for  histological  details  consult  Nussbaum  and  Lebrun).  On 
the  other  hand,  development  will  readily  proceed  in  the  absence  of 
the  jelly,  for  as  Hluchovski  has  shown  it  is  disintegrated  by  exposure 
to  ultra-violet  light  and  may  thus  be  removed  without  harming  the 

The  swelling  which  takes  place  in  the  gelatinous  covering  when 
the  eggs  are  shed  into  the  water  was  studied  as  long  ago  as  1824 
by  Prevost  &  Dumas,  who  measured  the  size  of  the  eggs  at  intervals 
after  they  were  laid.  Their  table  is  as  follows : 

Hours  after  laying 

Diameter  of  egg  (mm.) 















They  observed  that  dyes  would  pass  through  the  jelly  as  soon  as 
it  had  swollen,  but  not  before.  Similar  work  by  Wintrebert  on 
Discoglossus  pinctus  gave  the  following  figures : 

after  laying 

Diameter  of  egg  (mm, 


2-5  X  2-3 


3-0  X  2-7 


3-3  X  3-0 


5-8  X  3-2 



As  regards  the  mineralogical  and  morphological  structure  of  the 
egg-shells  of  the  lower  animals,  a  good  deal  is  known,  and  for  full 
detail  the  reviews  of  Prenant  and  of  Biedermann  should  be  referred 
to.  The  majority  of  reptile  egg-shells  have  their  calcium  carbonate 
in  the  form  of  calcite,  as  Kelly;  Schmidtt,  and  Meigen  have  shown, 
but  the  two  first-named  investigators  discovered  that  the  tgg- 
sheUs  of  chelonia  were  of  aragonite,  and  later  Lacroix  observed 
a  similar  phenomenon  in  the  case  of  certain  saurians.  The  tgg- 



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326  THE   UNFERTILISED   EGG  AS   A  [pt.  m 

membranes  of  snake's  eggs  which  show  all  variations  as  to  lime-content 
(see  Table  9)  are,  as  Kelly  has  shown,  composed  of  amorphous  and 
unstable  calcium  carbonate.  The  eggs  of  gastropods,  such  as  Helix, 
Ampullaria,  Bulimus,  Amphidromus,  etc.,  are,  as  Turpin  {Helix  aspersa) 
and  Rose  {Helix  pomatia) ,  besides  the  workers  mentioned  above,  have 
demonstrated,  like  those  of  birds  in  having  their  lime  in  the  form 
of  calcite.  For  a  general  theory  explaining  these  differences  see  the 
paper  of  Prenant. 

The  shells  of  eggs  may  also  contain  calcium  phosphate.  In  the 
hen  and  in  birds  generally  there  is  very  little,  but  the  globules  seen 
in  their  egg-shells  are  believed  to  be  calcium  phosphate,  though  no 
analysis  has  given  a  figure  of  more  than  i  per  cent,  of  this  salt. 
In  other  eggs,  however,  there  may  be  more;  thus  Gmelin  found 
7-3  per  cent,  in  the  egg-shells  of  a  tortoise,  and  Kelly  noted  its 
presence  also  in  those  of  Bulimus  and  Lophohelia,  though  she  gives  no 
analytical  figures. 

It  is  interesting  to  note  that  the  mineralogical  form  of  lime  in  the 
egg-shell  may  vary  during  the  development  of  the  embryo;  thus 
Kelly  says  that  the  shell  of  many  full-grown  mollusca  is  conchite, 
while  that  of  their  respective  embryos  and  eggs  is  calcite.  Kelly  found 
that  the  organic  substance  was  a  remarkably  constant  proportion 
of  the  shells  of  mollusca,  reptilia  and  birds  (see  Table  9).  Some  egg- 
coverings  contain  almost  no  water  at  all  (birds),  others  have  more 
than  the  egg-contents,  as  has  been  shown  for  the  trout's  egg  by 
Kronfeld  &  Scheminzki  (membrane  75  per  cent.,  egg  66  per  cent.). 

By  far  the  commonest  substance  of  which  egg-membranes  are  com- 
posed is  keratin,  though  this  protein  seems  to  take  many  forms,  and 
not  to  have  exactly  the  same  properties  in  different  situations.  The 
earlier  workers  were  content  to  assert  the  presence  of  it  on  the  basis 
merely  of  solubility  tests.  Thus  in  1874  Schenk  studied  the  egg-shell  of 
Raia  quadrimaculata,  and  decided  that  it  was  95  per  cent,  keratin  after 
the  application  to  it  of  the  protein  colour  reactions  and  an  examina- 
tion of  its  behaviour  towards  various  solvents.  The  same  conclusion 
was  arrived  at  by  the  same  methods  by  Hussakov  &  Welker  for  the 
egg-cases  of  Raia  erinacea,  and  the  Port  Jackson  shark,  Heterodontus 
philippi.  The  keratin  of  these  egg-cases  was  insoluble  in  all  solvents 
except  acid  and  alkali.  They  found  that  sulphur  was  present,  but 
no  phosphorus,  and  they  were  unable  to  find  any  reducing  sugar 
after  total  hydrolysis.    Irvine,  using  an  optical  test  for  chitin,  found 


none  in  elasmobranch  egg-cases.  Krukenberg  in  1885  decided  that 
the  egg-case  of  Scyllium  stellare  was  of  a  keratinoid  nature,  because 
of  its  percentage  composition,  in  which  he  found  a  marked  amount 
of  sulphur.  He  observed  the  interesting  fact  that  the  egg-cases  of 
this  fish,  while  still  in  the  uterus  of  the  parent  animal,  would  dissolve 
in  pepsin  and  trypsin,  while  after  they  were  laid  they  would  not 
dissolve  in  solutions  of  either  enzyme.  He  also  isolated  tyrosine  and 
leucine  firom  the  keratin  of  the  egg-cases  of  Scyllium  stellare.  He  made 
very  similar  researches  on  the  egg-cases  of  Scyllium  canicula  and 
Myliobatis  aquila,  finding  that  they  possessed  rather  different  properties 
and  seemed  to  be  of  different  constitution;  thus  on  hydrolysis  he 
recovered  a  great  deal  of  leucine  and  hardly  any  tyrosine  from  the 
keratin  of  Scyllium  canicula,  while  from  the  keratin  of  Myliobatis  the 
yields  were  precisely  reversed.  The  latter  substance  was  also  con- 
siderably more  resistant  to  digestion  than  the  former,  and  Krukenberg 
considered  that  the  former  was  not  a  keratin  at  all.  He  had  already 
decided  (wrongly,  as  it  turned  out)  that  the  shell-membrane  of  the 
hen's  egg  was  mucin,  not  keratin,  and  now  he  concluded  that  this 
also  applied  to  the  egg-case  oi Scyllium  stellare,  as  well  as  to  that  ofLoligo 
vulgaris,  of  which  he  made  a  separate  examination.  He  thought  it 
possible  also  that  the  jelly  which  surrounds  the  egg  in  the  ovo viviparous 
selachians  might  be  a  mucin  too,  especially  as,  according  to  Schenk,  it 
was  not  precipitated  by  chromic  acid,  and  he  himself  found  that  it  was 
extremely  resistant  to  digestion  by  enzymes.  This  material  has  received 
no  further  chemical  investigation  since  the  time  of  Krukenberg. 

Other  workers  who  identified  the  proteins  of  egg-membranes 
by  the  aid  of  colour  tests  and  solubility  reactions  were  Leuckart, 
who  showed,  as  far  as  anything  could  be  shown  with  such  preliminary 
methods,  that  the  membranes  of  planarian  eggs  were  of  chitin,  and 
Yoshida  &  Takano  and  Jammes  &  Martin,  who  drew  a  similar  con- 
clusion about  the  coats  of  the  eggs  of  Ascaris  lumbricoides,  which  they 
found  were  readily  soluble  in  gastric  juice  or  in  any  acid.^  The 
case  of  the  parasitic  nematodes  is  of  special  interest,  for  the  chitinous 
membrane  does  not  arise  until  after  the  fertilisation  of  the  egg,  being, 
therefore,  in  a  sense,  analogous  to  the  fertilisation  membranes  of 
echinoderms.  Whether  the  chitin  is  formed  as  it  is  required  during 
these  early  stages,  or  whether  it  is  already  present  in  the  unfertilised 
egg-cell  in  some  soluble  form,  is  uncertain.    Faure-Fremiet  in  an 

^  See  also  Campbell  on  the  chitin  of  insect  egg-membranes. 

328  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

attempt  to  throw  light  on  this  question,  prepared  pure  samples  of 
chitin  from  the  newly  fertilised  eggs  ofAscaris  megalocephala  by  boiling 
them  with  strong  potash,  and  identified  the  chitin  chemically, 
isolating  glucosamine  hydrochloride  from  it.  Remembering  that 
Weinland  showed  that  chitin  is  probably  formed  from  glycogen 
during  insect  metamorphosis,  Faure-Fremiet  estimated  the  glycogen 
in  the  Ascaris  eggs  before  and  after  fertilisation.  Before  fertilisation 
there  was  an  average  amount  of  20  gm.  per  cent,  dry  weight,  but 
afterwards  only  4-67,  the  extreme  values  being  5-91  and  3-23,  so 
that  no  less  than  17  per  cent,  of  glycogen  had  disappeared.  Estima- 
tions of  chitin  in  the  egg-envelopes  after  fertilisation  gave  results  of 
between  8-3  and  10-7  per  cent,  dry  weight  of  glucosamine  (calculated 
as  glycogen)  with  an  average  of  9-23.  The  total  glucose,  then,  in  the 
fertilised  eggs  was  12-83  to  15-08,  as  against  20-0  in  the  unfertilised 
ones,  a  loss  of  7  to  9  per  cent.  All  the  glucose  lost,  therefore,  could 
not  have  transformed  itself  into  chitin,  but  must  have  had  some  other 
destination,  perhaps  butyric  and  valerianic  acid  if  Weinland's  view  is 
correct.  The  eggs  o^  Ascaris  have  also  an  " ovospermatic  membrane", 
but  for  the  discussion  of  the  significance  of  this  reference  should  be 
made  to  the  memoir  of  Faure-Fremiet,  and  nothing  is  known  about 
it  chemically.  Their  third  membrane,  the  internal  one,  would  seem 
to  be  composed  to  a  large  extent  of  ascaristerol  (see  p.  352),  for  the 
histological  evidence  demonstrates  a  collection  of  the  ascaristerol 
globules  at  the  periphery  of  the  cytoplasm.  After  fertilisation,  Faure- 
Fremiet  found  the  saponification  number  of  ascaristerol  lowered  from 
199  to  145,  from  which  he  concluded  that  its  constitution  had  been 
slightly  altered.  Zavadovski  has  also  described  the  egg-shells  of  many 
nematodes.  • 

Neumeister,  who  found  more  than  5  per  cent,  of  sulphur  in  the 
shells  of  the  reptiles,  Calotes  jubatus,  Ptychozoon  homalocephalus,  and 
Crocodilus  biporcatus,  concluded  that  they  consisted  of  a  true  keratin, 
and  the  reactions  given  by  the  egg-membrane  protein  of  a  mono- 
treme,  Echidna  aculeata,  led  him  to  the  same  conclusion  in  that  case 
also.  Table  9  gives  the  figures  which  he  obtained  for  the  calcium 
and  other  constituents  of  some  of  these  egg-shells,  as  well  as  the 
very  similar  investigations  of  Wicke  &  Brummerstadt  on  Alligator 
sclerops.  From  these  fragmentary  results,  it  would  seem  that  the  egg- 
membrane  protein  is  here  keratin,  and  a  quantity  of  calcium  is 
secreted  into  the  membrane  by  the  animal,  varying  in  amount  from 


90  per  cent,  to  10  per  cent,,  according  to  the  species.  Again,  the 
egg-membrane  of  the  Brazihan  gastropod  studied  by  RofFo  &  Correa 
is  said,  on  the  basis  of  qualitative  tests  only,  to  be  a  true  keratin, 
containing  no  reducing  sugar  and  associated  with  no  other  sub- 
stances, save  2*45  per  cent,  of  ash.  It  contained  calcium  the  amount 
of  which  did  not  vary  during  development. 

The  transparent  horny  egg-membrane  of  the  selachian  Mustelus  ^ 
laevis,  which  disappears  half-way  through  the  development  of  the  ■ 
embryo,  has  also  been  investigated  by  Krukenberg,  who  compared 
it  with  the  egg-membrane  of  the  grass-snake,  Tropidonotus  natrix.  The 
former  resembled  the  shell-membrane  of  the  hen's  egg  rather  than 
the  true  keratin  of  the  Myliobatis  egg-case.  The  latter  seemed  to  have 
some  of  the  properties  of  elastin  and  some  of  those  of  keratin ;  from 
it  he  was  able  to  isolate  a  reducing  carbohydrate  as  well  as  glycine, 
tyrosine  and  leucine. 

Krukenberg  was  also  one  of  the  earliest  workers  to  make  quantita- 
tive investigations  on  this  subject.  His  figures  for  the  protein  of  the 
egg-shells  of  Murex  trunculatus  and  the  whelk  Buccinum  undatum,  which 
are  given  in  Table  33,  led  him  to  make  a  new  class  of  such  substances, 
the  conchiolins.  As  no  data  exist  for  the  sulphur  content  of  most 
of  these  proteins,  it  is  impossible  to  say  whether  they  are  keratins 
or  not,  and  the  whole  subject  needs  re-investigation.  About  five  years 
later,  Engel  also  investigated  the  egg-membrane  protein  of  Murex, 
and,  obtaining  0-5  per  cent,  of  sulphur  from  it,  concluded,  its  other 
properties  taken  into  account,  that  it  was  a  keratin.  Engel  also  agreed 
with  Hilger,  whose  figures  for  the  egg-membrane  of  the  snake, 
Coluber  natrix  (see  Table  30),  suggested  an  elastin  as  its  principal 
component.  He  had  not  been  able  to  find  any  sulphur  in  it.  About 
the  same  time,  Wetzel  examined  the  conchiolin  in_the_egg-shells  of, 
Mytilus  edulis,  and  obtained  from  it,  after  hydrolysis,  leucine,  tyrosine, 
glycine, Various  hexone  bases  and  ammonia,  but  no  phenylalanine. 

The  first  efforts  at  quantitative  discrimination  between  egg-mem- 
brane proteins  were  contented  with  ascertaining  the  elementary 
composition ;  thus  von  Fiirth  analysed  the  protein  of  Loligo  vulgaris 
eggs  in  this  way  (39  per  cent,  glucosamine),  and  Verson,  and  later 
Tichomirov,  decided  that  the  egg-shell  of  the  silkworm,  Bombyx  mori, 
was  a  keratin-like  body  (3-7  per  cent,  of  sulphur),  though,  owing  to 
its  unusual  properties,  they  called  it  chorionin.  Of  these  two  last- 
named  analyses,  it  is  probable  that  Tichomirov's  is  the  more  accurate. 

330  THE   UNFERTILISED   EGG   AS   A  [pt.  m 

for  he  was  more  careful  to  remove  all  the  adhering  silk  than  was 
Verson,  and  Farkas'  independent  work  agrees  rather  with  his.  It  is, 
at  any  rate,  clear  that  the  shell-substance  of  the  silkworm's  egg  is  not 
chitin.  According  to  Lavini  the  inorganic  constituents  of  the  silk- 
worm egg-shell  are  potassium  silicate,  sulphate,  and  carbonate,  to 
the  exclusion  of  all  other  salts. 

The  work  of  Pregl  and  of  Buchtala  in  1908  is  perhaps  the  most 
thorough  investigation  of  the  amino-acid  distribution  of  an  egg- 
membrane  protein.  The  figures  they  obtained  are  given  in  Table 
34.  The  keratin  of  the  egg-case'  of  Scyllium  stellar e  was  the  only 
one  of  which  they  made  a  complete  amino-acid  analysis ;  for  that 
of  Pristiurus  melanostoma  and  Scyllium  canicula  they  only  determined 
the  cystine  content  and  large  groups  such  as  the  monoamino-acid 
nitrogen.  Scyllium  ovokeratin  seemed  to  follow  very  closely  in  its 
constitution  the  ovokeratin  of  the  hen,  according  to  the  figures  of 
Abderhalden  &  Ebstein,  which  have  already  been  discussed,  but 
separated  itself  off  very  sharply  from  it  on  account  of  its  high  tyrosine 
content.  The  ovokeratin  of  the  tortoise  Testudo  graeca,  which  had 
been  investigated  two  years  previously  by  Abderhalden  &  Strauss, 
was  again  different,  having  no  tyrosine,  but  a  very  high  percentage 
of  proline.  As  far  as  this  work  goes,  it  would  seem  right  to  con- 
clude that,  though  the  eggs  of  different  species  may  use  similar 
proteins  in  their  external  membranes,  the  constitution  of  these  proteins 
may  vary  very  considerably. 

The  work  of  Steudel  &  Osato,  and  of  Osato,  however,  brought  a 
new  factor  into  the  problem.  Their  analyses  of  the  egg-membrane 
protein  of  the  herring's  egg,  which  are  shown  in  Tables  34,  38  and  39, 
gave  results  which  differed  from  the  usual  keratin  figures,  but  which 
very  closely  approached  the  analyses  which  they  were  making  at 
the  same  time  of  the  ichthulin  of  the  herring's  egg.  Thus  the  amide 
nitrogen  (2-05  per  cent.)  was  lower  than  any  of  the  keratins,  but 
approximated  instead  to  the  i-8i  per  cent,  of  herring  ichthulin.  What 
appeared  to  be  the  case  on  a  general  survey  turned  out  to  be  certainly 
so  when  the  amino-acid  distribution  was  examined,  for  the  two  sets 
of  figures  almost  exactly  corresponded.  The  properties  of  the  egg- 
membrane  protein  and  the  minute  amount  of  sulphur  in  it  precluded 
its  classification  as  a  keratin,  and  the  fact  that  no  reducing  sugar 
could  be  discovered  among  its  breakdown  products  was  convincing 
evidence  against  its  being  a  mucin.    Osato  suggested  that  it  was 

Table  34.   Distribution  of  amino-acids  in  egg-proteins. 

Amide  N     ... 







Aspartic  acid 

Glutamic  add 



Cystme        ... 

Hiiiudinc     ... 


Lysine         ... 

Total  di-amino 
Total  mono-am 
Non-amino  N  c 

ii      Scl 



Present       19'40  — 


4.4  _  ^ 


































50-7  — 






—  None 











































6 1 -55 



simply  an  insoluble  modification  of  ichthulin.  As  he  pointed  out, 
industrial  use  has  long  been  made  of  insoluble  forms  of  proteins, 
such  as  casein,  and  there  was  no  reason  why  the  egg-membranes 
of  certain  eggs,  at  any  rate,  should  not  be  insoluble  modifications 
of  the  proteins  of  their  yolks.  Steudel  &  Osato  also  suggested  that 
the  ovomucoid  of  the  egg-white  of  the  hen  might  be  a  phylogenetic 
reminiscence  of  the  mucoprotein  with  which  the  amphibian  egg  is 
surrounded.    For  a  review  of  this  work  see  Steudel. 

The  eggs  of  salps  and  tunicates  are  surrounded  by  a  coat  of  very 
much  smaller  cells  which  act  as  some  sort  of  protection  for  the 
developing  embryo  inside.  Zavattari  has  demonstrated  histochemi- 
cally  the  presence  of  an  abundance  of  glycogen  in  these  test  cells, 
and  believes  that  they  have  a  nutritive  function.  If  so,  this  would 
be  a  third  case  where  such  an  active  participation  of  the  shell  or 
case  in  embryonic  metabolism  would  have  been  noted,  the  two  others 
being  the  abstraction  of  calcium  from  the  shell  of  the  hen's  egg,  and 
the  contribution  of  amino-acids  by  the  egg-case  of  the  silkworm. 

A  good  deal  is  known  about  the  osmotic  and  other  properties  of 
the  membranes  of  amphibian  and  fish  eggs,  but  these  are  so  intimately 
associated  with  the  physico-chemical  processes  taking  place  during 
development  that  consideration  of  them  will  be  postponed  to  Sec- 
tion 5.  It  will  suffice  to  mention  here  the  experiments  of  Peyrega, 
who  found  that  the  egg-cases  of  Scyllium  canicula  were  permeable 
to  salt.  He  fitted  up  osmometers  with  small  pieces  of  the  case  as 
the  membranes,  and  observed  that  it  took  about  20  days  to  establish 
osmotic  equilibrium  with  respect  to  solutions  of  sodium  chloride 
about  as  strong  as  sea  water,  when  distilled  water  was  put  on  the 
other  side.  These  egg-cases  have  also  been  shown  by  Needham  & 
Needham  to  be  permeable  to  urea  and  ammonia. 

1-13.    Proteins  and  other  Nitrogenous  Compounds 

The  principal  protein  substance  which  is  found  to  occur  in  the 
eggs  of  all  known  animals  closely  resembles  the  vitellin  of  the 
hen's  egg.  It  has  even  been  found,  according  to  Chatton,  Parat  & 
Lvov,  in  the  food-reserves  of  infusoria.  The  early  analyses  of  the  eggs 
of  the  pike  by  Vauquelin  in  181 7,  of  the  barbel  {Cyprinus  barbus)  by 
Dulong  d'Astafort  in  1827,  and  of  the  trout  [Salmo  fario  and  Cyprinus 
carpio)  by  Morin  in  1823,  ^^^  to  no  more  than  the  view  that  an 
albuminous  substance  w£is  present  in  them.    But  with  the  work  of 

332  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

Gobley  on  the  hen's  egg,  which  has  already  been  described,  a  more 
solid  basis  for  comparison  was  achieved,  and  Valenciennes  &  Fremy, 
in  a  memoir  which  received  a  prize  from  the  Academy  of  Sciences 
and  which  was  translated  into  English,  proceeded  to  examine  the 
eggs  of  as  many  species  as  were  available  to  them.  Gobley's  only 
excursion  into  comparative  chemical  embryology  had  been  a  detailed 
analysis  of  the  carp's  egg,  published  in  1850,  but  he  had  not  been  slow 
to  point  out  the  differences  between  this  analysis  and  that  of  the  hen's 
egg.  His  figures  are  shown  in  Tables  2,  30  and  33,  where  it  will  be 
seen  that  he  got  a  value  of  15-76  per  cent,  protein  (wet  weight)  for 
the  hen,  and  14-23  per  cent,  for  the  carp,  but  31-43  per  cent,  fat 
for  the  hen  and  only  2-57  per  cent,  fat  for  the  carp.  The  carp's  egg 
had,  he  found,  about  10  per  cent,  more  water  than  the  yolk  of  the 
hen's  egg,  but  only  a  third  of  the  lipoid  substances. 

Fremy  &  Valenciennes  specially  directed  their  attention  to  the 
protein  fraction,  and  attempted  to  discover  whether  the  vitellin  was 
the  same  in  all  eggs.  For  the  most  part  they  relied  on  histological 
appearances  (the  "dotterplattchen"  were  greatly  discussed  at  this 
time),  but  they  also  examined  the  solubility  relationships  of  the 
proteins  from  each  egg,  and  in  some  cases  subjected  the  purified 
substances  to  elementary  analysis.  The  figures  they  obtained  for  the 
different  compounds  are  all  given  in  Table  33,  and  the  eggs  they 
investigated  in  Table  35.  They  were  able  to  isolate  a  number  of 
vitellin-like  proteins,  soluble  in  salt  solution  and  precipitated 
by  the  addition  of  water.  They  compared  vitellin  with  fibrin, 
and  concluded  that  the  two  substances  were  almost  identical,  in 
spite  of  slight  differences  in  the  analytical  figures — "for  bodies 
of  this  nature",  they  said,  "which  are  not  crystallisable  and 
insoluble  in  water  and  which  are  therefore  very  difficult  to  purify, 
where  is  the  chemist  who  could  answer  for  i  per  cent,  of  nitrogen  in 
an  elementary  organic  analysis?"  Ichthin,  which  they  isolated  from 
fish  eggs,  differed  from  vitellin  by  not  becoming  an  opaque  mass 
when  placed  for  a  long  time  in  boiling  water,  and  by  giving  a 
violet  instead  of  a  blue  colour  when  treated  with  boiling  hydrochloric 
acid.  Ichthidin,  another  product  offish  eggs,  differed  from  ichthin  in 
being  soluble  in  water.  Ichthulin,  the  third  member  of  the  group, 
differed  from  the  others  in  not  being  soluble  in  all  dilutions  of  saline, 
but  in  being  precipitated  from  the  aqueous  extract  by  further  ad- 
dition of  water.  As  for  emydin,  it  closely  resembled  ichthin,  and  it  is 

SECT.    l] 



not  easy  to  see  why  Valenciennes  &  Fremy  did  not  identify  it  with 
that  substance.  The  remaining  egg-proteins,  which  they  did  not 
further  investigate,  they  referred  to  under  the  generic  name  of 

Table  35.   Investigations 

AvES  Callus  domesticus 


of  Valenciennes  &  Fremy. 



Raia  clavata 


Torpedo  martnorata 


Scyllium  canicula 


Galeus  canis 


Alustelus  laevis 


Squatina  angelus 


Raia  fullonica 


Raia  rubus 



Cyprinus  carpio 

Ichthidin  and  ichthulin 

Labrax  lupus 

Ichthulin  and  ichthidin 

Alugil  chelo 

Scomber  scombrus 

Pleuronectes  maximus 

Pleuromctes  solea 

Solea  armorica 

Unidentified  species 

of  salmon 





Testudo  mauritanica 


Cistudo  europaea 


Unidentified  species 

of  lizard 







„       (?) 












Ar-achnida  and  Insecta           — 





Not  albumen 

The  differences  between  the  compositions  which  Valenciennes  & 
Fremy  found  for  these  substances  are  not  great,  and  it  is  very  doubtful 
whether  they  are  more  than  modifications  of  the  same  substance, 
especially  as  these  workers  admittedly  had  great  difficulty  in  ob- 
taining pure  preparations.  But  the  problem  of  the  identity  of  the 
vitellins  is  not  yet  settled.  The  later  investigations  are  all  grouped 
together  in  Table  33,  and  the  differences  between  the  preparations 
can  easily  be  seen  to  be  small.  The  work  of  Plimmer  &  Scott 
proved  that  ichthulin  is  a  phosphoprotein  closely  allied  to  vitellin. 
Among  the  more  interesting  observations  must  be  mentioned 
those  of  Levene  &  Mandel;  Levene,  and  Walther,  on  ichthulic  acid 
obtained  from    the   ichthulins    of  various   fish    eggs    by    digestion 

334  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

with  pepsin  and  other  methods.  These  with  their  very  high 
phosphorus  content  approach  closely  the  "  paranucleins "  or 
vitellic  acids  obtained  from  the  vitellin  of  the  hen's  yolk  by 
Levene  &  Alsberg  and  others.  Evidently  there  are  several  possible 
stages  of  breakdown,  for  Walther's  ichthulic  acid  only  contains  2-8  per 
cent,  of  phosphorus,  while  that  of  Levene  has  as  much  as  10-4. 
Here,  also,  however,  there  are  great  variations;  thus,  while  nearly 
all  the  ichthulins  studied  have  from  o-6  to  i  -9  per  cent,  of  phosphorus, 
the  preparation  of  Steudel  &  Takahashi  from  the  herring's  egg  has 
only  0-014  P^r  cent.  In  the  yolk  of  a  dogfish  egg,  Zdarek  found  no 
less  than  three  proteins,  the  third  of  which  may  possibly  correspond 
with  Konig  &  Grossfeld's  albumen  class. 

In  1908  Alsberg  &  Clark  claimed  that  phosphorus  was  quite  absent 
from  the  principal  protein  of  the  egg  of  an  ovoviviparous  selachian, 
Squalus  acanthias,  but  some  twenty  years  later  I  re-examined  the 
question  and  obtained  without  difficulty  o-6  per  cent,  from  selachian 
ichthulin  (derived  from  the  same  species).  This  yolk  also  contains  a 
second  protein,  thuichthin,  corresponding  closely  in  properties  and 
constitution  with  the  ovolivetin  of  the  hen  studied  by  Kay  &  Marshall 
(see  Tables  10  a  and  33). 

Gray  has  studied  the  properties  of  the  ovoglobulin  or  ichthulin 
of  Salmo  fario.  If  the  yolks  are  poured  into  water,  a  dense  white  clot 
is  formed  and  the  water  becomes  cloudy.  The  precipitate  is  soluble, 
however,  in  acids,  alkalies  and  neutral  salts.  When  the  egg-cell 
dies,  the  egg  becomes  opaque,  and  this  must  certainly  be  due  to  the 
precipitation  of  the  globulin,  for  by  placing  dead  white  eggs  in 
normal  sodium  chloride  solution  they  rapidly  become  clear  and 
resemble  normal  eggs,  but  regain  their  opacity  when  removed  to 
distilled  water.  The  clearing  process  takes  15  minutes  but  the 
precipitation  takes  i|  hours.  Evidently  the  dead  protoplasmic 
membrane  can  no  longer  retain  in  the  egg  the  electrolytes  necessary 
for  solution  of  the  ichthulin. 

Further  work  on  the  properties  of  teleostean  ichthulin  was 
done  by  Runnstrom.  1-5  parts  of  egg  "Pressaft"  having  been  added 
to  1-28  parts  of  water  and  the  ichthulin  precipitated,  the  effect 
of  various  ions  on  its  solubility  was  tried.  The  anions  placed  them- 
selves in  the  order: 

SON  >  I  >  NO,  >  SO.  >  CI  >  acetate. 


Thus  for  2  c.c.  of  potassium  chloride  solution,  0-3  c.c.  of  distilled 
water  had  to  be  added  to  get  coagulation,  but  to  2  c.c.  of  KSCN 
solution,  as  much  as  6-4  c.c.   The  cations  went  as  follows: 

Ca  >  Mg  >  Sr  >  K   and    Na. 

The  egg-white  of  the  dogfish  egg  was  thought  by  Brande  in  1810 
to  be  identical  with  the  jelly  surrounding  the  egg  of  the  frog,  but 
whether  the  former  really  consists  of  mucin  and  not  albumen  cannot 
be  definitely  stated,  for  no  work  has  since  been  done  on  it.  However, 
my  wife  and  I,  in  our  work  on  the  eggs  oi Scyllium  canicula,  frequently 
observed  a  coagulation  of  the  egg-white  with  acetic  acid,  which  would 
point  to  the  latter  possibility. 

The  proteins  of  the  echinoderm  egg  have  never  been  properly 
investigated.  Vies,  Achard  &  Prikelmaier  have  estimated  from  cata- 
phoresis  experiments  that  the  average  isoelectric  point  of  the  Para- 
centrotus  lividus  egg-proteins  lies  between  5-0  and  5-8  pH.,  but  their 
grounds  for  this  figure  are  not  free  from  criticism. 

Vies  &  Gex,  in  some  interesting  experiments,  have  studied  the 
normal  unfertilised  sea-urchin's  tgg  spectrophotometrically.  The 
absorption  spectrum  of  the  normal  egg  has  peaks  or  bands  at 
wave-lengths  of  490,  395,  370,  315,  and  230  Angstrom  units,  and  a 
marked  trough  between  260  and  240  A.  This  curve  is  very  peculiar, 
for  on  the  one  hand  it  shows  much  transparency  in  the  ultra-violet 
although  most  organic  substances  do  not,  while  on  the  other  hand 
there  is  nothing  at  all  corresponding  to  the  bands  of  absorption 
about  A  275  which  all  proteins  give.  This  absorption  is  brought 
about  by  the  cyclic  amino-acids  in  the  protein  molecule,  and  it  is 
quite  impossible  that  these  should  be  altogether  absent  from  the 
egg-proteins  of  the  sea-urchin.  Vies  &  Gex  considered  various 
technical  possibilities  which  might  explain  these  effects,  but  did 
not  think  that  any  of  them  would  account  for  what  was  perhaps  the 
most  remarkable  part  of  the  investigation,  namely,  the  finding  that 
on  cytolysis  ("white")  a  perfectly  definite  and  clear  absorption 
spectrum  for  protein  revealed  itself  In  the  intact  egg,  then,  this 
must  be  masked  by  something  else.  Speculation  on  the  nature  of 
this  mechanism  would  be  easy,  for  all  kinds  of  eflfects  might  be 
responsible,  e.g.,  formation  of  complexes,  reduction  equilibria,  and 
satisfaction  in  vivo  but  not  in  vitro  of  residual  valencies  in  the  protein 
molecule.    If  this  very  interesting  work  should  lead  in  the  future 

336  THE   UNFERTILISED   EGG  AS  A  [pt.  iii 

to  a  revivification  in  a  subtler  form  of  the  old  biogen  molecule 
theory  (though  it  is  to  be  hoped  that  it  will  not),  not  only  as  regards 
the  egg-cell  but  as  regards  protoplasm  in  general,  we  shall  at  any 
rate  possess  in  the  spectrophotometer  a  powerful  means  of  studying 
the  untouched  normal  cell-interior. 

Doubt  exists  with  respect  to  the  presence  of  reducing  carbohydrate 
in  the  ichthulin  molecule.  Levene  &  Mandel  obtained  minimal 
quantities  of  laevulinic  acid  from  their  cod  ichthulin,  but  this 
finding  was  associated  with  the  presence  of  purine  bases.  Six  years 
earlier  Levene  had  been  unable  to  find  a  trace  of  glucosamine  in 
cod  ichthulin.  Similar  negative  results  were  obtained  by  Steudel  & 
Takahashi  on  herring,  and  by  Hammarsten  on  perch,  ichthulin. 
But  the  presence  of  glucosamine  in  notable  amounts  has  been 
reported  for  Torpedo  ichthulin  by  Rothera,  and  for  carp  ichthulin  by 
Walther.  While  it  is  possible,  and  even  probable,  that  ichthulins 
from  different  fish  eggs  may  vary  much,  it  would  be  very  desirable 
to  know  to  what  extent  this  is  the  case,  and  a  comparative  study 
of  ichthulins  is  much  needed.  As  we  have  seen  Levene  &  Mori  have 
isolated  a  trisaccharide  from  avian  vitellin. 

Closely  allied  to  the  question  of  the  presence  of  carbohydrate 
groupings  in  the  ichthulin  molecule  is  the  equally  disputed  problem 
of  the  presence  of  purine  bases  in  the  undeveloped  tgg.  We  have 
already  seen  that  Miescher's  identification  of  nucleoprotein  with 
vitellin  was  quite  erroneous,  and  have  described  how  he  was  set 
right  by  Kossel.  For  the  hen's  &gg,  it  is  now  fairly  clear  that  nucleins 
are  present  only  in  exceedingly  small  amounts  at  the  beginning  of 
development,  not  exceeding,  for  instance,  i  or  2  per  cent,  of  the  total 
nitrogen  or  phosphorus.  But  there  has  been  more  difficulty  in  de- 
ciding what  is  the  real  state  of  affairs  in  the  eggs  of  fishes  and 
aquatic  invertebrates.  Walther  (carp),  Hugounenq  (herring),  Linnert 
(sturgeon),  and  Hammarsten  (perch),  all  examined  the  ichthulin  of 
these  eggs  for  nucleic  acid,  and  all  failed  to  find  the  least  trace  of  it. 
Henze,  on  the  other  hand,  working  with  the  whole  tgg  of  the 
cephalopod.  Sepia  officinalis,  isolated  considerable  amounts  of  purines 
together  with  no  less  than  1-15  gm.  per  cent,  of  a  pentose.  Tscher- 
norutzki  a  little  later  found  that  10  per  cent,  of  the  total  phosphorus 
of  the  herring's  egg  could  be  accounted  for  as  nucleoprotein  phos- 
phorus, and  the  nucleoprotein  itself  amounted  to  i-ig  gm.  per  cent, 
dry  weight.  Masing;  Tichomirov,  and  Needham  &  Needham  reported 


quite  similar  results  with  the  sea-urchin's  egg,  the  egg  of  the  silkworm 
and  the  eggs  of  various  Crustacea,  echinoderms  and  an  annelid.  In 
the  sea-urchin  egg  purine  bases  were  found  accounting  for  6  per  cent, 
of  the  total  nitrogen  as  nucleoprotein  nitrogen,  while  in  the  case  of 
Bombyx  there  were  20  mgm.  per  cent,  dry  weight.  Again,  Levene  & 
Mandel  isolated  from  their  ichthulic  acid  in  1907  0-344  P^^^  cent,  of 
guanine,  0-307  per  cent,  of  adenine,  0-360  per  cent,  of  uracil  and 
0-309  per  cent,  of  thymine.  Mandel  &  Levene  were  also  able  to 
isolate  nucleic  acid  from  cod's  eggs.  It  would  certainly  appear  from 
this  evidence  as  if  ichthulin  and  vitellin  may  be  associated  with  small 
quantities  of  nucleic  acid.  In  this  connection  it  is  of  interest  that 
Calvery  has  evidence  that  the  chick  embryo  can  synthesise  "yeast-" 
as  well  as  animal  nucleic  acid.  Steudel  &  Osato  have  also  obtained 
guanine  and  adenine  from  herring's  eggs,  but  this  was  in  the  non- 
protein nitrogen  fraction,  and  there  was  therefore  no  evidence  from 
their  work  that  any  preformed  nucleic  acid  was  a  constituent  of  the 
egg.  The  most  exhaustive  investigation  of  the  problem  was  that  of 
Konig  &  Grossfeld,  who  in  1913  set  out  definitely  to  clear  up  the 
discrepancy.  As  perhaps  might  have  been  expected,  they  found  that 
they  could  isolate  purine  bases  after  hydrolysis  from  all  the  fish  eggs 
they  studied,  but  only  in  small  quantity;  their  results  are  shown  in 
Table  36.  The  question  of  nuclein  synthesis  by  the  developing 
embryo  will  be  discussed  in  relation  to  these  findings  in  Section  I0'3. 

Table  36.   Investigations  of  Konig  &  Grossfeld. 

Total  purine  bases  isolated 

dry  weight 

Cod    ... 
Pike   ... 

I -060 

But  the  exact  relationship  between  the  nuclein  and  the  vitelHn 
remains  exceedingly  obscure.  It  is  possible  that  in  one  and  the 
same  egg  there  may  be  more  than  one  modification  of  vitelHn, 
apart  altogether  from  the  insoluble  form  suggested  by  Steudel  & 
Osato.    All   the  knowledge   that   we   possess    at   the   present  time 



[PT.  Ill 

on  this  point  is  of  an  unsatisfactory  histological  nature,  and  any 
discussion  of  it  must  inevitably  include  an  unprofitable  proportion 
of  guesswork.  Thus,  Jorgensen  differentiated  histologically  between 
two  substances  which  seemed  to  be  present  in  the  unripe  egg  of 
Patella  vulgata,  ergastoplasm  No.  i  and  ergastoplasm  No.  2,  one  at 
least  of  which  was  responsible  for  the  formation  of  the  vitelline 
globules.  Faure-Fremiet  &  Garrault  identified  ergastoplasm  No.  i 
with  the  mitochondria,  and  ergastoplasm  No.  2  with  the  fatty  con- 
stituents of  the  yolk.  But  if  two  forms  of  vitellin  existed,  one  in  loose 
combination  with  a  nuclein  and  the  other  free,  the  staining  reactions 
of  histological  elements  mainly  constituted  by  one  or  other  of  these 

Table  37. 













and  date 








McCrudden  (1921) 










A  little 
















Levene  (1901) 







Walther  (1891) 







Hammarsten  (1905) 







Valenciennes  & 
Fremy  (1854) 








Gobley  (1850) 

substances  would  very  likely  differ,  and  it  is  possible  that  an  explana- 
tion on  these  lines  may  in  the  future  correlate  the  chemistry  with  the 
histology  of  the  yolk.  The  vitellin  question  has  been  in  a  measure 
reviewed  by  McCrudden,  whose  table  (given  in  Table  37)  illustrates 
the  difficulty  of  summing  up  the  findings  of  investigators  at  all 

The  amino-acid  analyses  (Table  34)  are  rather  more  interesting. 
We  have  data  for  the  vitellins  of  the  herring,  the  trout,  the  cod, 
and  the  sturgeon  among  fishes,  the  frog  among  amphibia,  the  grass- 
snake  among  reptiles,  and  Hemifusus  tuba,  a  gastropod.  To  this  may 
be  added  amino-acid  analyses  of  the  mixed  egg-proteins  of  the  sea- 
urchin  egg  and  the  eggs  of  the  brook-trout  and  the  giant  salamander, 
as  well  as  the  albumens  of  cod  and  sturgeon  and  the  mucoprotein 
of  Hemifusus.  If  the  fish  ichthulin  analyses  of  Iguchi  or  Hugounenq 
be  compared  with  those  of  Table  1 1  for  the  vitellin  of  the  hen,  no 
very  marked  differences  can  be  observed,  although  the  predominancy 


of  arginine  and  lysine  over  histidine,  which  is  a  constant  feature  of 
the  ichthulins,  reaches  greater  values  in  the  latter  than  in  the  case 
of  bird  vitellin  (see  Table  38).  Again,  bird  vitellin  always  shows 
a  notable  proportion  of  proline  and  leucine,  and  this  is  also  the  case 
with  the  vitellins  of  the  lower  animals  (e.g.  10  per  cent,  of  leucine 
in  gastropod  vitellin,  19  per  cent,  in  snake  vitellin  and  9  per  cent, 
in  herring  ichthulin),  though  the  amount  of  proline  is  usually  not  so 
great.  The  only  instance  of  a  real  divergence  between  bird  and  other 
vitellins  would  appear  to  be  the  glutamic  acid  content,  which  is 
always  high  in  the  former,  although  this  amino-acid  is  absent  from 
the  latter. 

Table  38.    Hexone  bases  of  yolk-proteins. 

In  gm.  %  original 
In  %  total  nitrogen  protein 


Species  Protein  Hist.      Arg.      Lysine    Hist.     Arg.    Lysine  and  date 

Herring           Ichthulin  2-45  I4"50  10-07  I'^S  6-33  7-40  Steudel  &  Takahashi  (1923) 

Egg-menibrane  3-99  14-41  7-51  2-09  6-35  5-55  Steudel  &  Osato  (1923) 

Hen                  Vitellin  —  —  —  i-go  7-46  4-81  Osborne  &  Jones  ( 1 909) 

Herring           Ichthulin  0-40  2-70  2-00  —  —  —  Hugounenq  (1904) 


Sturgeon         Ichthulin  0-47  0-97  o-oi  —  —  —  Konig  &  Grossfeld  (1913) 

Cod                  Ichthulin  0-55  0-54  0-02  —  —  —             ,,               ,, 

Trout               Ichthulin  0-54  0-41  o-oi  —  —  —              ,,              ,, 

Gastropod       Ichthulin  None  3-73  0-86  —  —  —  Komori  (1926) 

Frog                Vitellin  1-14  1-06  0-29  —  —  —  Galimard  (1904) 


Snake              Vitellin  0-30  0-32  1-45  —  —  —                      ,, 

If  now  Table  39  is  considered,  it  will  be  seen  that  variations  are 
present  in  the  general  analysis  of  these  proteins,  but  that  they  tend 
to  cancel  each  other  out  among  the  groups.  Thus  the  mono-amino- 
acid/di-amino-acid  ratio  is  very  constant  indeed  in  different  ichthulins, 
although  Rothera  himself  considered  that  he  was  dealing  with  two 
entirely  different  proteins,  the  vitellin  of  the  Torpedo  egg  and  that 
of  the  sturgeon.  It  is  unfortunate  that  Komori's  examination  of 
gastropod  vitellin  was  confined  to  the  estimation  of  the  amino-acids 
by  isolation,  and  did  not  include  a  van  Slyke  determination  of  the 
relative  amounts  of  mono-amino  and  di-amino  acids.  In  contra- 
distinction to  the  ichthulins,  the  mixed  egg-proteins  studied  by  Russo 
and  Gortner  show  more  variation,  though  the  former's  values  for  two 
sea-urchin  ^gg  proteins  agree  well  with  the  usual  vitellin  figure. 
Masing,  however,  was  not  able  to  find  any  phosphoprotein  phos- 



[PT.  Ill 

phorus  in  sea-urchin  eggs,  and  Needham  &  Needham  found  only 
very  little.  It  is  interesting  to  note  that  the  ratio  is  subject  to  large 
fluctuations  among  the  keratins  of  the  egg-cases.  As  for  the  albumens 
which  Konig  &  Grossfeld  isolated  from  the  eggs  of  the  sturgeon  and 
the  cod,  they  seem  to  approach  in  their  composition,  in  so  far  as  data 
for  the  hexone  bases  permit  one  to  form  a  conclusion,  the  ovoal- 
bumen  in  the  hen's  egg.  The  8  per  cent,  of  tyrosine  obtained  from  the 
sturgeon  ovoalbumen  is,  however,  remarkable.  The  mucoprotein  which 
Komori  found  around  the  eggs  of  the  gastropod  Hemifusus  tuba,  and 
which  he  partially  analysed,  is  not  sufficiently  well  characterised  to 
be  compared  except  roughly  with  the  mucoprotein  of  the  amphibian 

Table  39. 

In  %  total  nitrogen 


Torpedo  {Torpedo  marmorata) 


Dogfish  (Scyllium  stellare) 

„        (Pristiurus  melanostoma) 
,,        (Scy Ilium  caniculd) 


Herring  ... 



Giant  salamander 





Mixed  egg- 
proteins  (total) 

Mixed  egg-pro- 
teins (coag.  only) 

Mixed  egg- 

Vitellin  (for  i 


1 6-43 



849    1-26      6o-20 









and  date 

Rothera  (1904) 
Buchtala  (1908) 

Steudel  &  Takahashi 

Steudel  &  Osato 

Russo  (1926) 

7-33  2-05      —  62-11  25-91  2-40 

—  284  45-70  17-30  2-64 

—  —        —  62-20  29-80  209              ,, 

1-82  —        —  61-55  28-25  2-18     Gortner  (1913) 

2-25        — 
1-63      S-55 

53-73    29-35    1-83 

67-10    25-10    2-67    Plimmer  (1908) 

The  general  distribution  of  nitrogenous  substances  in  the  eggs  of 
the  lower  animals  is  shown  in  Tables  40  and  41.  Pigorini's  investiga- 
tion of  the  silkworm  egg  is  suggestive,  but  his  data  about  the 
different  protein  fractions  are  insufficient  to  enable  us  to  form  any 
judgment  on  their  relation  to  those  so  well  known  in  the  bird's  egg. 
The  very  large  amount  of  mucoprotein  in  the  silkworm  ovum  is 
certainly  remarkable.  In  Table  41  are  placed  the  few  data  which 
we  have  on  the  relative  amounts  of  protein  and  non-protein  nitrogen 
in  different  eggs,  and  the  way  the  protein  is  divided  between  keratin, 
albumen,  and  ichthulin  or  vitellin.  Clearly  enough  there  is  great 
variation,  and  a  rough  dichotomy  into  two  groups,  one  in  which  the 


non-protein  nitrogen  accounts  for  from  14  to  35  per  cent,  of  the  total 
nitrogen,  and  one  in  which  it  only  accounts  for  less  than  10  per  cent, 
of  the  total  nitrogen.  It  is  evident  from  the  work  of  Konig  &  Gross- 
feld  that  all  the  fishes  examined  belong  to  the  first  of  these  categories, 
although  within  the  group  there  are  wide  divergences,  such  as  the 
minute  amount  of  albumen  apparently  present  in  the  trout's  egg 
and  the  low  non-protein  nitrogen  of  the  herring's  egg.  Good  agree- 
ment is  to  be  noted  between  the  results  of  Levene  and  Konig  & 
Grossfeld,  who  all  worked  on  the  cod;  and,  although  nothing  con- 
cerning the  non-protein  nitrogen  can  be  gathered  from  the  figures  of 
Kensington  and  Hugounenq,  their  results  do  show  general  agreement 
as  regards  the  partition  of  nitrogen  among  the  proteins.  The  only 
reptile  on  whose  eggs  work  has  been  done  which  could  be  incorporated 
in  the  table  is  the  grass-snake,  and  there,  although  no  non-protein 
nitrogen  figures  are  available,  it  is  interesting  to  note  the  very  high 
proportion  of  keratin. 

Table  40. 

Silkworm  (Bomfryx:  mon).   (Pigorini,  1Q23.) 
In  %  of  total  protein 


Protein  sol.  in  water  but  not 
Protein  sol.  in  Protein  sol.  in  Protein  sol.  in  coagulable  by  heat,  and 

distilled  water  10  °„  salt  sol.  dilute  alkalies  yielding  glucosamine  on 

(albumen)  (vitellin)  (nucleoprotein)  hydrolysis  (ovomucoid) 

29-20  8-57  11-45  5090 

The  second  principal  group,  consisting  of  those  eggs  which  have 
a  relatively  much  lower  percentage  of  non-protein  nitrogen,  contains 
two  members,  the  hen  and  the  silkworm.  The  former  may  be  said 
with  a  high  degree  of  probability  to  be  characteristic  of  all 
nidifugous  birds,  and  perhaps  of  nidicolous  ones  also,  but  whether 
the  latter  is  at  all  representative  of  the  centrolecithal  insect  eggs 
may  be  considered  doubtful.  The  sole  insect  egg  which  has  been 
investigated  chemically,  so  far,  is  that  of  the  silkworm,  and  until 
more  evidence  is  available  the  hen  and  the  silkworm  will  have  to 
be  placed  together  in  this  second  group  without  comment.  It  is 
significant  that,  in  the  hen's  case,  the  percentage  of  albumen  is 
greater  than  in  any  other,  a  fact  obviously  referable  to  the  large 
amount  of  egg-white  present  in  that  egg.  Finally,  it  is  of  interest 
that  the  sea-urchin's  egg  seems  to  have  a  protein/non-protein  nitrogen 
ratio  very  like  that  of  the  fishes,  but  situated  on  the  low  protein 
edge  of  their  limits  of  variation. 


THE   UNFERTILISED   EGG   AS   A  [pt.  iii 

Table  41.   Distribution  of 


%  wet 






(by  diff.) 


of  egg- 
brane   Albumen 




bases  and 





Carp  ... 











































































Sea-urchin  (Strongylo- 

centrotus  lividus) 


















Grass-snake  (Tropido- 

notus  natrix) 








Fresh- water  gar 











Hen  (average  results) 

whole  egg 
Turtle  (Thalassoclielys 

corticata)  yolk 











*  With  so  %  mucoprotein  and 

Within  the  non-protein  nitrogen  fraction  itself  there  are  some 
fragmentary  data  for  the  distribution,  as  may  be  seen  from  Table  42 . 
Unidentified  compounds  usually  account  for  from  20  to  35  per  cent, 
of  the  total  non-protein  nitrogen,  and  free  amino-acids  for  approxi- 
mately half  of  it.  Among  those  identified  by  Steudel  &  Osato  were 
histidine,  arginine,  lysine  and  cystine.  The  ammonia  may  vary  from 
4  to  25  per  cent.,  and  the  purine  bases  from  15  to  40  per  cent. 
As  far  as  can  be  seen  at  present,  the  hen's  egg  seems  to  possess 
the  greater  part  of  its  non-protein  nitrogen  in  the  basic  fraction. 
The  most  interesting  point  brought  out  by  the  table  is  probably  the 
significant  quantity  of  urea  shown  to  be  present  by  the  analyses  of 
Steudel  &  Osato,  amounting  to  no  less  than  half  of  the  total  non- 
protein nitrogen,  and  it  is  possible  that  a  good  deal  of  the  unidentified 
nitrogen  of  Konig  &  Grossfeld  might  be  accounted  for  in  this  way. 
The  presence  of  nitrogenous  excretory  products  in  the  undeveloped 
egg,  though  at  first  sight  paradoxical,  is  nevertheless  undoubtedly  a 
fact  in  the  case  of  some  aquatic  organisms.  The  hen's  egg  contains 
hardly  a  trace  of  urea  at  the  beginning  of  development  but  that  of 
a  selachian  fish  contains  a  good  deal  (see  Section  9- 1 1 ) . 


the  nitrogen  in  eggs. 

Gm.  %  dry  weight  (ash  free) 

^ A . ^ 

%  of  the  total  nitrogen  Egg- 

, — ^ ■ — \  Pro-  mem-  Free 

Free  tain  Pro-  brane  Nitro-  bases  and 

Protein      Ker-     Albu-  Ichthu-  amino-  (N  x  tein  (by  pro-  Albu-  Ichthu-    gen      amino-                                Investigate 

total        atin       men        Hn        acids  625)  diflF.)       tein  men       Hn     (direct)     acids      Fat       Ash  and  date 

66-9         121               548            331  85-37  92-37  1119  50-64           13-65      30-54      7-64        —     Konig  &  Gr 


70-96        11-35      721      52-4      2904  82-75  95-93  10-90  6-92     50-25     13-08      27-87      407       —         „ 

85-20  15-7  0-49      790  1485  80-56     89-25  5-10        0-44  70-48  12-89  13-24  IO-7S  — 

86-15  12-70      9-15      543  13-9  89-52     85-75  10-88  16-43  46-53  14-33  "-Qi  14-25  — 

68-41  10-50       i-oi      469  315  8933      94-84  9-97  10-48  44-51  14-29  29-88  5-55  —  „ 

(loo-o?)  —  11-70     880  —  87-80      —  —  10-30  77-5  —  —  4-50  7-50  Kensington  ( 

(loo-o?)  2-7              973  —  __  —  —          —  —  —  —  —  Hugounenq 

62-0  —          —          —  379            —           _  —  —          —  —  —  —  —  Russo  (1926) 

94-0  —        27-4  8-05      6-04*       —  —  —  —  —  —  —  —  —      Monzini(i9: 

Pigorini  (ic 
96-0  —  —  —  3-98      65-25        —  —  —  —  —  —  —  —      Russo  (1922) 

(loo-o?)     66-0        3-74     30-2         —  —         —         —         —         —         —         —         —         —      Galimard  (19 

66-0  —  —  —        33-0        68-09        —  —  —  —  —  —  —  —      Levene  (i89( 

_  ___  —  _________      Nelson  &  Gi 

96-4  406      49-8        42-5        366         —  —  —  —  —  —  —  —  —  — 

Q8-5  —  —  —  1-5  —  —  —  —  —  —  —  —  —      Tomita  (1921 

chorionin  in  addition. 

As  is  well  known,  these  fishes  have  a  special  relation  to  this  sub- 
stance. In  1858  Stadeler  &  Frerichs  isolated  "kolossale  Quantitaten 
von  Harnstoff"  from  the  organs  of  plagiostomes,  obtaining  a  solid 
mass  of  urea  nitrate  when  they  added  nitric  acid  to  their  final  con- 
centrates. One  liver  of  an  adult  Scy Ilium  canicula  gave  them  2  oz.  of 
urea,  and  similar  high  figures  were  reported  for  Acanthias  vulgaris. 
Teleostean  fishes,  however,  and  the  cyclostome,  Petromyzon  planeri, 
yielded  practically  no  urea,  at  any  rate  not  more  than  would  be 
present  in  mammalian  tissues.  Stadeler  confirmed  the  selachian 
results  on  Raia  batis  and  clavata  and  on  Torpedo  marmorata  and  ocellata. 
In  1 86 1  Schulze  repeated  and  confirmed  Stadeler's  work  on  Torpedo, 
and  in  1888  Krukenberg  published  an  extensive  work  on  the  subject, 
in  which  he  related  his  unsuccessful  attempts  to  demonstrate  urea 
in  the  bodies  of  teleosts  {Lophius  piscatorius.  Conger  vulgaris,  Acipenser 
sturio),  a  cyclostome  [Petromyzon  fluviatilis  and  Ammocoetes)  and  a 
cephalochordate  (Amphioxus  lanceolatus) ,  although  he  found  large 
amounts  of  it  in  the  bodies  of  elasmobranch  fishes  [Scyllium  stellare, 
Mustelus  vulgaris  and  laevis,  Acanthias  vulgaris,  Squatina  angelus,  Torpedo 
marmorata,    Myliobatis    aquila)    and    in    the    holocephalic    Chimaera 

344  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

monstrosa.  Particularly  interesting  were  his  experiments  with  eggs — 
he  isolated  considerable  amounts  of  urea  from  a  5  cm.  embryo  of 
Mustelus  laevis,  and  from  the  yolk  of  Scyllium  stellare  and  Myliobatis 
aquila  eggs,  but  he  could  find  none  in  the  surrounding  jelly  or  "white  ". 
An  Ggg  ofPristis  antiquorum  yielded  3920  mgm.  per  cent,  (wet  weight) 
and  a  Torpedo  ocellata  egg  1 740  mgm.  per  cent.  An  Acanthias  vulgaris 
embryo  1 7  cm.  long  had  3360  mgm.  per  cent,  in  its  muscles,  1800  mgm. 
per  cent,  in  its  liver,  and  2640  mgm.  per  cent,  in  its  unused  yolk. 
Other  work  on  urea  in  selachians  was  done  by  Grehant  and  by 
Rabuteau  &  Papillon. 

Table  42.   Distribution  of  non-protein  nitrogen  in  eggs. 

%  of  total  non-protein  N  (including  purine  N) 

g-|    z       §      iz      g      2       -g      I      I     |Z 

w.«   „       „  ^  2^  c  S  "G  2  o  op  Investigator 

Species  HSo?      cq  <fe^         P  U  D         U         hUa  and  date 

Herring —  198  —      44-3      359        —        —        —  —  —  Konig  &  Grossfeld  (1913) 

Carp        ...         ...  —  39-8  —      36-1      24-1        —        —        —  —  —             >>                 >, 

Sturgeon             ...  —  25-2  13-6      55-4      189         —         —         —  —  —              ,,                  ,, 

Herring  ...          ...  2060       244  67      21-6         —       519  None     18-3  —  —  Steudel  &  Osato  (1923); 

Steudel  &  Takahashi  (1923) 

Herring 1443  16-91  23-42    41-65    1802      —         —         —  —  —  Yoshimura  (1913) 

Silkworm            ...  440  —  4-44    54-30    34-60      — -         —         —  610  6-7  Russo  (1922) 

Hen  (aver,  figures)  —  88-80  4-22      7-04     —      None  None  Trace  —  —                       — 

Fresh- water  gar  299  92-00  —          4-02     —          —         —          4-0  —  —  Nelson  &  Greene  (1921) 

(not  ripe) 

More  light,  however,  was  thrown  on  the  reasons  for  this  richness 
in  urea  when  in  1897  Bottazzi  working  on  the  osmotic  pressure  offish 
blood,  found  that  the  elasmobranchs  differed  fundamentally  from 
teleosts  in  being  isotonic  with  sea  water. 



Selachians      Torpedo  marmorata  —2-26° 

Trygon  violacea  —2-44° 

Teleosteans    Charax  pimtazzo  —1-04° 

Serranus  gigas  —  i  -03° 

Bottazzi  observed  that  the  selachian  osmotic  pressure  would  corre- 
spond to  some  3-9  per  cent,  sodium  chloride  but  laid  no  emphasis  on 
the  fact  that  selachian  blood  did  not  contain  anything  like  so  much 
ash.  It  was  left  for  Rodier  to  show  that  the  difference  was  made  up 
almost  wholly  by  urea.  Duval  has  since  found  that  the  salts  alone 
would  only  give  an  osmotic  pressure  of  A  —  i-o6°.  "High  blood- 
urea",  as  Smith  says,  "is  a  phyletic  character  of  the  orders  Selachii 


and  Batoidei",  and  its  osmotic  function  was  well  shown  by  the 
reciprocal  relation  between  salts  and  urea  which  Smith  found  to 
hold  in  selachian  tissues  and  fluids. 


mgm.  % 

Smith  (1929) 


Dogfish  {Mustelus  canis) 


Denis  (1913) 


Dogfish  {Mustelus  canis) 


Sandshark  {Carcharias  littoralis)... 


Skate  {Raia  erinacea) 




Mackerel  {Scomber  scombrus) 


Goosefish  {Lophius piscatorius)     ... 


Flounder  {Paralichthys  dentalus) 


In  view  of  all  these  facts  it  is  not  surprising  that  Needham  &  Need- 
ham  in  1928  found  about  5  mgm.  of  urea  nitrogen  present  in  the 
Scyllium  canicula  egg  at  the  beginning  of  development ;  and  888  mgm. 
per  cent,  of  urea  in  the  undeveloped  Acanthias  vulgaris  egg.  Gori,  again, 
found  7 10  mgm.  in  undeveloped  Torpedo  eggs.  But  since  urea  accumu- 
lation is  closely  confined  to  elasmobranchs  it  is  unlikely  that  the  results 
of  Steudel  &  Takahashi  and  of  Konig  &  Grossfeld  can  be  interpreted 
as  being  due  to  urea. 

The  presence  of  urea  has  also  been  reported  in  the  undeveloped 
eggs  of  "ants  and  flies"  (in  small  quantities)  by  Fosse.  Further 
details  would  be  desirable  here. 

There  is  reason  to  believe  that  nitrogenous  substances  other  than 
those  already  mentioned  are  present  in  certain  eggs.  Thus  Yoshimura 
and  Poller  &  Linneweh  isolated  trimethylamine,  tetramethylene- 
diamine  and  choline  from  fresh  herring  eggs,  and  there  is  a  certain 
probability  that  fish  eggs  also  contain  betaine.  As  the  characteristic 
smell  of  fish  is  due  to  these  amines  and  related  substances,  this  is  not 
very  surprising.  Brieger  is  said  to  have  found  neuridine  in  fish  eggs, 
and  Schii eking  isolated  spermine  from  echinoderm  eggs  in  1903. 
Taurine  and  glycine  were  found  in  echinoderm  eggs  by  Kossel  & 

Of  the  manner  of  formation  of  ichthulin  in  the  maturation  of  the 
ovum  we  know  absolutely  nothing.  Paton  &  Newbigin  concluded 
from  a  very  few  analyses  that  the  phosphorus  was  brought  to  the 
ovaries  from  the  muscle  of  the  salmon  as  inorganic  phosphorus,  but, 
in  view  of  what  is  now  known  about  the  organic  phosphorus  com- 
pounds of  blood,  this  appears  rather  unlikely. 

346  THE   UNFERTILISED   EGG  AS   A  [pt.  in 

I '14.    Fats,  Lipoids  and  Sterols 

Studies  on  the  fatty  substances  of  the  undeveloped  eggs  of  different 
animals  have  resulted  in  much  interesting  information.  There  has 
been,  of  course,  a  great  body  of  histological  work,  and  the  yolks 
of  all  kinds  of  eggs  have  been  repeatedly  subjected  to  microscopic 
examination  (for  example,  Kaneko's  study  on  the  silkworm);  but, 
in  spite  of  many  attempts,  I  have  not  succeeded  in  finding  more  than 
a  few  hints  in  this  literature  which  are  of  value  to  the  chemical  worker. 
This  subject  has  been  dealt  with  in  a  general  way  by  Ransom  and 
by  Dubuisson,  to  whose  papers  those  interested  in  the  histological 
aspects  of  yolk  must  be  referred.  Of  the  way  in  which  the  fat  and 
the  protein  are  intermingled  in  the  yolk  we  know  practically  nothing, 
and  it  would  be  most  desirable  to  investigate  the  yolk  with  the 
methods  which  modern  colloidal  chemistry  has  developed.  But  that 
the  association  between  fat  and  protein  indicated  by  the  histological 
evidence  is  not  very  close  is  shown  by  the  interesting  centrifugation 
experiments  of  McClendon  on  the  amphibian  egg.  If  the  egg  of  the 
frog  is  centrifuged  for  five  minutes  under  the  right  conditions,  it 
separates  into  three  perfectly  distinct  layers,  the  upper  one  being 
oily  and  yellow,  the  middle  one  translucent,  colourless  and  proto- 
plasmic, and  the  lowest  one  black,  containing  practically  all  the  yolk. 
By  using  a  considerable  number  of  eggs,  McClendon  was  enabled 
to  obtain  suflticient  material  for  the  chemical  analysis  of  each  layer. 
The  figures  he  obtained  are  shown  in  Table  43.  It  is  evident  from 
a  slight  inspection  of  his  results  that  the  upper  layer  is  composed 
mainly  of  neutral  fats  and  a  little  lecithin,  and  the  middle  layer  of 
water,  salts  and  protein,  with  no  fats  or  lipoids.  The  lowest  and  much 
the  largest  layer  is  made  up  of  the  vitellin  (ranovin  or  batrachiolin) 
together  with  the  major  part  of  the  lecithin.  It  is  interesting  that  the 
association  between  the  phosphoprotein  and  the  lipoid  was  the  only 
one  that  centrifuging  could  not  break,  for,  as  we  have  already 
seen,  the  observation  of  a  loose  lecitho-vitellin  combination  in 
the  hen's  egg  is  very  old.  McClendon  found  that  mitotic  figures 
were  all  present  in  the  middle  layer,  and  that  this  centrifuging 
produced  a  variety  of  monstrous  embryos.  He  was  led  to  regard 
the  protoplasm  of  the  egg  as  constant  in  composition  throughout, 
but  "anisotropic  as  regards  its  axes,  in  other  words  crystalline 
in  structure". 

SECT.    l] 



McClendon  extended  his  observations  to  the  egg  of  the  sea-urchin, 
Arbacia  punctulata.  Separated  by  centrifugal  force,  this  egg  divided 
itself  into  four  layers,  as  Lyon  had  already  described,  {a)  a  layer  of 
yolk  bodies  and  red  pigment  granules  extending  from  the  centrifugal 
end  about  half-way  to  the  equator,  {b)  a  layer  of  similar  yolk  bodies 
but  without  the  pigment  granules,  {c)  a  translucent  fluid  layer  ex- 
tending almost  to  the  centripetal  pole  and  containing  the  nucleus, 
and  finally  {d)  a  very  opaque  layer  or  cap  of  minute  volume,  sitting 
on  the  centripetal  pole.  When  the  crushed  eggs  were  centrifuged, 
the  material  separated  into  two  layers,  {a)  and  {b)  being  indistin- 
guishable, centrifugal  and  containing  the  egg-membranes,  and 
[c)  centripetal,  {d)  not  being  perceptible.  McClendon  analysed  the 
layers  in  the  same  manner  as  those  of  the  frog's  egg — the  figures 
are  given  in  Table  43. 

Table  43. 
McClendon' s  figures  (1909). 




in  the  layers 


,  of 








dry  weight 







t!  2 

c  t< 

—1  1) 



*->  tJ 
a  0 

&  2 


Layers  of  centri- 



Upper  centripetal 












fuged    egg   of 

(fatty  or  oily) 

Rana  pipiens 



Middle  (proto- 















Lower  centrifugal 













Layers   of  centri- 



Centripetal  (proto- 













fuged  egg  of  ^r- 


bacia  punctulata 



Centrifugal  (yolky) 













A  short  consideration  of  them  shows  that  centrifugal  force  is  not 
nearly  so  successful  in  separating  the  egg  of  the  sea-urchin  into 
chemically  unlike  layers  as  it  is  in  the  case  of  the  frog.  This  fits  in 
perhaps  with  the  long-established  fact  that  centrifugal  force  inter- 
feres far  less  with  normal  development  in  the  sea-urchin's  egg  than 
it  does  in  the  frog's  egg  (Morgan  and  Lyon).  It  was  very  noticeable 
that,  whereas  the  frog's  egg  separated  out  into  layers  of  markedly 
different  water-content,  this  did  not  take  place  in  the  sea-urchin's 
egg.  In  the  case  of  the  centrifuged  frog's  egg,  again,  there  were  big 
differences  between  the  phosphorus  contents  of  the  different  layers, 
but  in  that  of  the  sea-urchin's  egg  this  only  applied  to  the  residues 
which  were  mainly  protein.   McClendon  surmised  that  the  inclusion 

348  THE   UNFERTILISED   EGG  AS   A  [pt.  iii 

of  the  membrane  proteins  in  the  centrifugal  layer  caused  this 

It  is  of  course  a  fact  of  the  first  importance  that  normal  develop- 
ment can  follow  centrifugation  and  this  will  receive  attention  later 
(see  Section  3  and  the  Epilegomena) .  I  shall  only  mention  here 
as  one  of  the  best  instances  of  this  phenomenon,  the  work  of 
Schaxel  on  the  axolotl  egg.  Here  centrifugation  caused  atypical 
discoidal  cleavage  which  nevertheless  resulted  in  a  normally  pro- 
portioned embryo.  Thus  normal  conclusions  can  follow  abnormal 
distribution  of  the  so-called  "organ-forming  substances".  For  further 
details  of  these  experiments,  see  Morgan  and  Bertalanffy. 

The  early  work  of  Gobley  o